On a dusty field in Israel's southern desert, the military is gearing up for the next battle against a familiar foe: Hezbollah guerrillas in Lebanon.

As the Syrian civil war intensifies, military planners are growing increasingly jittery that the fighting could spill over into Israel, potentially dragging the Islamic militant group that is allied with President Bashar Assad into the fray. After battling Hezbollah to a stalemate in 2006, the Israeli military says it has learned key lessons and is prepared to inflict heavy damage on the group if fighting begins again.

The Israel-Lebanon border has remained largely quiet since that last war. But Hezbollah has since replenished its arsenal and has waged a shadow war with Israel around the world. The fall of the Syrian leader or alternatively an Israel strike against Hezbollah's other main patron, Iran, could spark another full-fledged war.

"There is an increase in tension because of Syria," a senior commander in the military's northern command said about a possible battle with Hezbollah. The commander, who traveled south to observe Thursday's exercise here, spoke on condition of anonymity in line with military protocol.

In 2006, weeks of Israeli air raids killed more than 1,000 people, including hundreds of Hezbollah fighters, and key infrastructure was destroyed. But the heavy onslaught failed to prevent Hezbollah from firing some 4,000 rockets into Israel, and the fighting ended in a U.N.-brokered truce.

While the truce has largely held, Israel says Hezbollah has systematically restocked its arsenal with tens of thousands of even more powerful rockets and missiles capable of striking virtually anywhere in the Jewish state. Israeli military officials frequently say it is only a matter of time before the next war erupts.

In the meantime, Israel and Hezbollah have fought a covert war outside the borders of their countries. In 2008, Hezbollah's top military commander Imad Mughniyeh was killed in a car bombing in the Syrian capital of Damascus, an attack widely thought to be the work of Israeli agents.

Hezbollah, for its part, is thought to be responsible for a bus bombing in a Bulgarian resort town last July that killed five Israeli tourists and their Bulgarian driver, as well as failed attempts to bomb Israeli diplomats in Thailand, India and Georgia.

Israeli military officials believe that Hezbollah, which is preoccupied with its own domestic problems and the precarious position of its Syrian ally, has no desire to reignite hostilities. But they say the Syrian civil war, as well as Israel's tensions with Iran, could easily upset the fragile balance.

As Assad's grip on power weakens, Israeli military planners fear that Syria, backed by Hezbollah, might try to open a new front in order to deflect attention. Israel also fears that sophisticated Syrian weapons, including a chemical arsenal, could be transferred to Hezbollah. Israel has all but confirmed it carried out an airstrike in Syria in January that destroyed a shipment of anti-aircraft missiles allegedly bound to Hezbollah.

Likewise, an Israeli attack on Iran would almost certainly draw a Hezbollah reprisal. Israel has repeatedly hinted it is prepared to attack Iran's nuclear installations if it determines that international sanctions and diplomacy have failed to curb the Iranian nuclear program. Israel and much of the West believe Iran is developing a nuclear weapon, a charge Iran denies.

Earlier this week, Israeli Prime Minister Benjamin Netanyahu warned of the potential link between Iran and Hezbollah.

"A nuclear-armed Iran would dramatically increase terrorism by giving terrorists a nuclear umbrella," he told members of the pro-Israel lobbying group American Israel Public Affairs Committee, known as AIPAC. "That means that Iran's terror proxies like Hezbollah ... will be emboldened to attack America, Israel and others because they will be backed by a power with atomic weapons."

Hezbollah's leader, Hassan Nasrallah, has warned that anyone who thinks Hezbollah is vulnerable because of Syria's civil war is mistaken. He also said the group has all the weapons it needs in case war breaks out with Israel, and it would not need to import them from allies Syria and Iran.

"The resistance will not be silent regarding any aggression against Lebanon," Nasrallah said last month.

Israel is also taking a fiercer tone, saying it will act with far less restraint than it did in 2006, when it took out electric grids, roads and city blocks during the monthlong war that was sparked by a deadly cross-border raid by Hezbollah. Military officials say entire villages that host Hezbollah's arsenal would be considered fair targets.

During Thursday's exercise, near the Revivim collective farm, scores of Israeli reservists in full battle gear participated in a drill meant to simulate Israel's capture of a strategic hill overlooking a southern Lebanese village.

In the drill, three tanks kicked up dust as they charged forward and fired live rounds. In front of them, groups of soldiers lay flat on the ground and opened fire with propped-up guns as other soldiers stormed up the hill. Their targets were small cutout cartoon heads meant to represent Hezbollah fighters.

On a nearby Israeli army base, reservists have also been practicing urban warfare recently on a set made to resemble an Arab village, complete with concrete homes, narrow alleyways and mosque minarets.

Military officials say that while Hezbollah has upgraded its capabilities, Israel has also made important offensive and defensive changes since 2006, when it came under heavy criticism for its lack of preparedness and perceived sloppy performance.

They say the military now possesses sophisticated real-time intelligence and upgraded drones. For any potential land operation, it has fortified its armored personnel vehicles, activated a new tank defense that can shoot down anti-tank rockets and recently deployed "Iron Dome," a defense system that shot down hundreds of rockets during a recent round of fighting against Hamas militants in the Gaza Strip.

Despite its arsenal and political clout in Lebanon, Hezbollah's maneuvering space has been significantly reduced in recent years.

Hezbollah still suffers from the fallout of the 2006 war, which many in Lebanon accused Hezbollah of provoking by killing and kidnapping Israeli soldiers from the border area. Since then, the group has come under increasing pressure at home to disarm. Though Hezbollah has been accused of fighting alongside the military in Syria, the group has largely been cautious with regards to the Syria conflict, knowing that any action it takes could backfire.

In addition, the group's reputation has been tarnished because its leader has supported Arab Spring uprisings in Tunisia, Libya and Egypt, but has backed the Assad regime in Syria.