In 2009, the deputy chief of mission of the U.S. embassy in Baku, Donald Lu, sent a cable to the State Department's headquarters in Foggy Bottom titled "Azerbaijan's discreet symbiosis with Israel." The memo, later released by WikiLeaks, quotes Azerbaijan's President Ilham Aliyev as describing his country's relationship with the Jewish state as an iceberg: "nine-tenths of it is below the surface."

Why does it matter? Because Azerbaijan is strategically located on Iran's northern border and, according to several high-level sources I've spoken with inside the U.S. government, Obama administration officials now believe that the "submerged" aspect of the Israeli-Azerbaijani alliance -- the security cooperation between the two countries -- is heightening the risks of an Israeli strike on Iran.

In particular, four senior diplomats and military intelligence officers say that the United States has concluded that Israel has recently been granted access to airbases on Iran's northern border. To do what, exactly, is not clear. "The Israelis have bought an airfield," a senior administration official told me in early February, "and the airfield is called Azerbaijan."

Senior U.S. intelligence officials are increasingly concerned that Israel's military expansion into Azerbaijan complicates U.S. efforts to dampen Israeli-Iranian tensions, according to the sources. Military planners, I was told, must now plan not only for a war scenario that includes the Persian Gulf -- but one that could include the Caucasus. The burgeoning Israel-Azerbaijan relationship has also become a flashpoint in both countries' relationship with Turkey, a regional heavyweight that fears the economic and political fallout of a war with Iran. Turkey's most senior government officials have raised their concerns with their U.S. counterparts, as well as with the Azeris, the sources said.

The Israeli embassy in Washington, the Israel Defense Forces, and the Mossad, Israel's national intelligence agency, were all contacted for comment on this story but did not respond.

The Azeri embassy to the United States also did not respond to requests for information regarding Azerbaijan's security agreements with Israel. During a recent visit to Tehran, however, Azerbaijan's defense minister publicly ruled out the use of Azerbaijan for a strike on Iran. "The Republic of Azerbaijan, like always in the past, will never permit any country to take advantage of its land, or air, against the Islamic Republic of Iran, which we consider our brother and friend country," he said.

But even if his government makes good on that promise, it could still provide Israel with essential support. A U.S. military intelligence officer noted that Azeri defense minister did not explicitly bar Israeli bombers from landing in the country after a strike. Nor did he rule out the basing of Israeli search-and-rescue units in the country. Proffering such landing rights -- and mounting search and rescue operations closer to Iran -- would make an Israeli attack on Iran easier.

"We're watching what Iran does closely," one of the U.S. sources, an intelligence officer engaged in assessing the ramifications of a prospective Israeli attack confirmed. "But we're now watching what Israel is doing in Azerbaijan. And we're not happy about it."

Israel's deepening relationship with the Baku government was cemented in February by a $1.6 billion arms agreement that provides Azerbaijan with sophisticated drones and missile-defense systems. At the same time, Baku's ties with Tehran have frayed: Iran presented a note to Azerbaijan's ambassador last month claiming that Baku has supported Israeli-trained assassination squads targeting Iranian scientists, an accusation the Azeri government called "a slander." In February, a member of Yeni Azerbadzhan -- the ruling party -- called on the government to change the country's name to "North Azerbaijan," implicitly suggesting that the 16 million Azeris who live in northern Iran ("South Azerbaijan") are in need of liberation.

And this month, Baku announced that 22 people had been arrested for spying on behalf of Iran, charging they had been tasked by the Islamic Revolutionary Guard Corps to "commit terrorist acts against the U.S., Israeli, and other Western states' embassies." The allegations prompted multiple angry denials from the Iranian government.

It's clear why the Israelis prize their ties to Azerbaijan -- and why the Iranians are infuriated by them. The Azeri military has four abandoned, Soviet-era airfields that would potentially be available to the Israelis, as well as four airbases for their own aircraft, according to the International Institute for Strategic Studies' Military Balance 2011.

The U.S. intelligence and diplomatic officials told me they believe that Israel has gained access to these airbases through a series of quiet political and military understandings. "I doubt that there's actually anything in writing," added a senior retired American diplomat who spent his career in the region. "But I don't think there's any doubt -- if Israeli jets want to land in Azerbaijan after an attack, they'd probably be allowed to do so. Israel is deeply embedded in Azerbaijan, and has been for the last two decades."

The prospect of Israel using Azerbaijan's airfields for an Iranian attack first became public in December 2006, when retired Israeli Brig. Gen. Oded Tira angrily denounced the George W. Bush administration's lack of action on the Iranian nuclear program. "For our part," he wrote in a widely cited commentary, "we should also coordinate with Azerbaijan the use of airbases in its territory and also enlist the support of the Azeri minority in Iran." The "coordination" that Tira spoke of is now a reality, the U.S. sources told me.

Access to such airfields is important for Israel, because it would mean that Israeli F-15I and F-16I fighter-bombers would not have to refuel midflight during a strike on Iran's nuclear facilities, but could simply continue north and land in Azerbaijan. Defense analyst David Isenberg describes the ability to use Azeri airfields as "a significant asset" to any Israel strike, calculating that the 2,200-mile trip from Israel to Iran and back again would stretch Israel's warplanes to their limits. "Even if they added extra fuel tanks, they'd be running on fumes," Isenberg told me, "so being allowed access to Azeri airfields would be crucial."

Former CENTCOM commander Gen. Joe Hoar simplified Israel's calculations: "They save themselves 800 miles of fuel," he told me in a recent telephone interview. "That doesn't guarantee that Israel will attack Iran, but it certainly makes it more doable."

Using airbases in Azerbaijan would ensure that Israel would not have to rely on its modest fleet of air refuelers or on its refueling expertise, which a senior U.S. military intelligence officer described as "pretty minimal." Military planners have monitored Israeli refueling exercises, he added, and are not impressed. "They're just not very good at it."

Retired Air Force Col. Sam Gardiner, who conducted a study for a think tank affiliated with the Swedish Ministry of Defense of likely Israeli attack scenarios in March 2010, said that Israel is capable of using its fleet of F-15I and F-16I warplanes in a strike on Iran without refueling after the initial top-off over Israel. "It's not weight that's a problem," he said, "but the numbers of weapons that are mounted on each aircraft." Put simply, the more distance a fighter-bomber is required to travel, the more fuel it will need and the fewer weapons it can carry. Shortening the distance adds firepower, and enhances the chances for a successful strike.

"The problem is the F-15s," Gardiner said, "who would go in as fighters to protect the F-16 bombers and stay over the target." In the likely event that Iran scrambled its fighters to intercept the Israeli jets, he continued, the F-15s would be used to engage them. "Those F-15s would burn up fuel over the target, and would need to land."

Could they land in Azerbaijan? "Well, it would have to be low profile, because of political sensitivities, so that means it would have to be outside of Baku and it would have to be highly developed." Azerbaijan has such a place: the Sitalcay airstrip, which is located just over 40 miles northwest of Baku and 340 miles from the Iranian border. Prior to the collapse of the Soviet Union, Sitalcay's two tarmacs and the adjacent facilities were used by a squadron of Soviet Sukhoi SU-25 jets -- perfect for Israeli fighters and bombers. "Well then," Gardiner said, after the site was described to him, "that would be the place."

Even if Israeli jets did not land in Azerbaijan, access to Azeri airfields holds a number of advantages for the Israel Defense Forces. The airfields not only have facilities to service fighter-bombers, but a senior U.S. military intelligence officer said that Israel would likely base helicopter rescue units there in the days just prior to a strike for possible search and rescue missions.

This officer pointed to a July 2010 joint Israeli-Romanian exercise that tested Israeli air capabilities in mountainous areas -- like those the Israeli Air Force would face during a bombing mission against Iranian nuclear facilities that the Iranians have buried deep into mountainsides. U.S. military officers watched the exercises closely, not least because they objected to the large number of Israeli fighters operating from airbases of a NATO-member country, but also because 100 Israeli fighters overflew Greece as a part of a simulation of an attack on Iran. The Israelis eventually curtailed their Romanian military activities when the United States expressed discomfort with practicing the bombing of Iran from a NATO country, according to this senior military intelligence officer.

This same senior U.S. military intelligence officer speculated that the search and rescue component of those operations will be transferred to Azerbaijan -- "if they haven't been already." He added that Israel could also use Azerbaijan as a base for Israeli drones, either as part of a follow-on attack against Iran, or to mount aerial assessment missions in an attack's aftermath.

Azerbaijan clearly profits from its deepening relationship with Israel. The Jewish state is the second largest customer for Azeri oil - shipped through the Baku-Tibilisi-Ceyhan pipeline -- and its military trade allows Azerbaijan to upgrade its military after the Organization for Cooperation and Security in Europe (OSCE) slapped it with an arms embargo after its six-year undeclared war with Armenia over the disputed Nagorno-Karabakh region. Finally, modernizing the Azeri military sends a clear signal to Iran that interference in Azerbaijan could be costly.

"Azerbaijan has worries of its own," said Alexander Murinson, an Israeli-American scholar who wrote in an influential monograph on Israeli-Azeri ties for Tel Aviv's Begin-Sadat Center for Strategic Studies. "The Baku government has expelled Iranians preaching in their mosques, broken up pro-Iranian terrorist groups, and countered Iranian propaganda efforts among its population."

The deepening Azeri-Israeli relationship has also escalated Israel's dispute with Turkey, which began when Israeli commandos boarded a Turkish ship destined for Gaza in May 2010, killing nine Turkish citizens. When Turkey demanded an apology, Israel not only refused, it abruptly canceled a $150 million contract to develop and manufacture drones with the Turkish military -- then entered negotiations with Azerbaijan to jointly manufacture 60 Israeli drones of varying types. The $1.6 billion arms agreement between Israel and Azerbaijan also left Turkish Prime Minister Recep Tayyip Erdogan "sputtering in rage," according to a retired U.S. diplomat.

The centerpiece of the recent arms deal is Azerbaijan's acquisition of Israeli drones, which has only heightened Turkish anxieties further. In November 2011, the Turkish government retrieved the wreckage of an Israeli "Heron" drone in the Mediterranean, south of the city of Adana -- well inside its maritime borders. Erdogan's government believed the drone's flight had originated in the Kurdish areas of northern Iraq and demanded that Israel provide an explanation, but got none. "They lied; they told us the drone didn't belong to them," a former Turkish official told me last month. "But it had their markings."

Israel began cultivating strong relations with Baku in 1994, when Israeli telecommunications firm Bezeq bought a large share of the nationally controlled telephone operating system. By 1995, Azerbaijan's marketplace was awash with Israeli goods: "Strauss ice cream, cell phones produced by Motorola's Israeli division, Maccabee beer, and other Israeli imports are ubiquitous," an Israeli reporter wrote in the Jerusalem Post.

In March 1996, then-Health Minister Ephraim Sneh became the first senior Israeli official to visit Baku -- but not the last. Benjamin Netanyahu made the trip in 1997, a high-level Knesset delegation in 1998, Deputy Prime Minister Avigdor Lieberman and Foreign Minister Tzipi Livni in 2007, Israeli President Shimon Peres in 2009, and Lieberman again, as foreign minister, this last February. Accompanying Peres on his visit to Baku was Avi Leumi, the CEO of Israel's Aeronautics Defense Systems and a former Mossad official who paved the way for the drone agreement.

U.S. intelligence officials began to take Israel's courtship of Azerbaijan seriously in 2001, one of the senior U.S. military intelligence officers said. In 2001, Israeli arms manufacturer Elbit Systems contracted with Georgia's Tbilisi Aerospace Manufacturing to upgrade the Soviet SU-25 Scorpion, a close air-support fighter, and one of its first customers was Azerbaijan. More recently, Israel's Elta Systems has cooperated with Azerbaijan in building the TecSar reconnaissance satellite system and, in 2009, the two countries began negotiations over Azeri production of the Namer infantry fighting vehicle.

Israeli firms "built and guard the fence around Baku's international airport, monitor and help protect Azerbaijan's energy infrastructure, and even provide security for Azerbaijan's president on foreign visits," according to a study published by Ilya Bourtman in the Middle East Journal. Bourtman noted that Azerbaijan shares intelligence data on Iran with Israel, while Murinson raised the possibility that Israelis have set up electronic listening stations along Azerbaijan's Iranian border.

Israeli officials downplay their military cooperation with Baku, pointing out that Azerbaijan is one of the few Muslim nations that makes Israelis feel welcome. "I think that in the Caucasian region, Azerbaijan is an icon of progress and modernity," Sneh told an Azeri magazine in July 2010.

Many would beg to differ with that description. Sneh's claim "is laughable," the retired American diplomat said. "Azerbaijan is a thuggish family-run kleptocracy and one of the most corrupt regimes in the world." The U.S. embassy in Baku has also been scathing: A 2009 State Department cable described Aliyev, the son of the country's longtime ruler and former KGB general Heydar Aliyev, as a "mafia-like" figure, comparable to "Godfather" characters Sonny and Michael Corleone. On domestic issues in particular, the cable warned that Aliyev's policies had become "increasingly authoritarian and hostile to diversity of political views."

But the U.S. military is less concerned with Israel's business interests in Baku, which are well-known, than it is with how and if Israel will employ its influence in Azerbaijan, should its leaders decide to strike Iran's nuclear facilities. The cable goes on to confirm that Israel is focused on Azerbaijan as a military ally -- "Israel's main goal is to preserve Azerbaijan as an ally against Iran, a platform for reconnaissance of that country and as a market for military hardware."

It is precisely what is not known about the relationship that keeps U.S. military planners up at night. One former CIA analyst doubted that Israel will launch an attack from Azerbaijan, describing it as "just too chancy, politically." However, he didn't rule out Israel's use of Azeri airfields to mount what he calls "follow-on or recovery operations." He then added: "Of course, if they do that, it widens the conflict, and complicates it. It's extremely dangerous."

One of the senior U.S. military officers familiar with U.S. war plans is not as circumspect. "We are studying every option, every variable, and every factor in a possible Israeli strike," he told me. Does that include Israel's use of Azerbaijan as a platform from which to launch a strike -- or to recover Israeli aircraft following one? There was only a moment's hesitation. "I think I've answered the question," he said.