NEGEV DESERT, Israel — For decades, the striking ridges and shady passes of the western Negev Desert along Israel’s border with Egypt were an alluring gateway to the pristine beaches of the Sinai Peninsula.

Today, though, from the Israeli side at least, the jagged landscape of red-brown mountains seems to cast longer shadows and has grown more menacing.

Israeli security officials point to an erosion of Egyptian sovereignty and authority in the vast, sandy expanses of the Sinai desert, particularly in the year since the Egyptian revolution. They say that Egypt’s attention has been more focused on events in Cairo.

Years of relative quiet were punctuated six months ago by a cross-border terrorist attack near the Israeli resort of Eilat that left eight Israelis dead. Since then, Israel’s anxiety has taken physical form as its defense establishment rushes to complete a 150-mile, 16-foot-tall steel border fence that will stretch all the way from Eilat up to Gaza.

“This is a hot border now,” said Lt. Col. Yoav Tilan, the deputy brigade commander in the area. “The major threat falls under the title of infiltration,” he added, in a briefing for reporters during a recent tour of the border zone.

Underscoring the tensions in the area, Israeli forces patrolling an as-yet-unfenced part of the border killed an unidentified infiltrator overnight on Monday during a firefight with a group of people suspected of being smugglers. Twice last month soldiers patrolling the border found bags filled with explosives, according to the Israeli military, dropped by smugglers who apparently scrambled back into Egypt.

The attack last August took place along an Israeli highway known as Route 12, which winds along the border. Israeli forces killed three of the assailants who had crossed into Israeli territory, and five Egyptian officers were accidentally killed by Israeli security forces as they chased down the attackers. Enraged Egyptians then ransacked the Israeli Embassy in Cairo, further shaking the 30-year-old peace between Israel and Egypt that was already under strain after the ouster of President Hosni Mubarak, Israel’s former ally.

A section of the road closest to the Egyptian positions — where the gunmen staged their ambush of an Israeli bus, private cars and army personnel — reopened to civilian daytime traffic for the first time on Sunday.

The strategically located Sinai, a buffer area between Israel and Egypt, became popular with Israelis after Israel seized it in the 1967 Middle East war. It remained so with those shunning package tourism even after the area was returned to Egypt after its 1979 peace treaty with Israel.

More recently, however, Israel’s counterterrorism bureau has issued dire travel advisories warning citizens against visiting Sinai. Reports from across the border tell of armed Bedouin tribesmen briefly kidnapping foreigners, heists occurring at tourist resorts and the repeated bombing of a pipeline that carries natural gas from Egypt to Israel.

Israeli military officials say that there are now hundreds of terrorists in Sinai, and that the militant activity mostly emanates from the Palestinian enclave of Gaza and, to a lesser extent, from global jihadist cells originating in North Africa. The officials say that ammunition and arms found at the site of the attack last August could be traced to Gaza.

Egyptians say the allegations of terrorist activity are wildly overblown. They acknowledge that the Sinai area has long provided a refuge for a certain number of militants. But after a recent military operation in the area, the Egyptian Interior Ministry — perhaps somewhat optimistically — pronounced it completely purged of militants.

“We have already denied that there is any presence of Al Qaeda in the governorate, or any other terrorist group for that matter,” said Gen. Abdel Wahab Mabrouk, the area’s governor.

He acknowledged, however, that since the revolution weapons had proliferated and that the police presence had receded across the country. Many others say that law enforcement has all but completely withdrawn from the Sinai, allowing it to become a hotbed of apolitical criminality. General Mabrouk’s own car was recently stolen.

He said he had no complaints about the Israelis protecting their border with a fence. But local Bedouin, speaking on condition of anonymity for fear of arrest, say they are incensed because it will interfere with their cross-border smuggling.

Others have long linked the crime in the Sinai to provisions in the 1979 peace treaty that limit the presence of Egyptian armed soldiers or police officers in the area. Hala Mustafa, editor of the state-run journal Democracy, argued that the Egyptian government might have deliberately relaxed its Sinai security to help persuade the Israelis to modify the treaty provision. Despite the tensions, the Israeli military says that members of its liaison unit in the area are in daily contact with their Egyptian counterparts.

But along this notoriously porous frontier, continually crisscrossed by Bedouin smugglers, military officials say it is increasingly difficult to distinguish between criminals, refugees, terrorists, friends or foes.

The Sinai, according to another senior Israeli commander, has become a “platform for criminals, terror activity, fugitives — anyone running away from their governments.”

The roughly 300,000 Bedouin tribesmen of the Sinai and their Bedouin kinsmen in southern Israel have nomadic roots and a traditional lack of respect for manmade borders. Lacking alternative sources of income and neglected by the authorities, they have long made the smuggling of goods and human trafficking a major part of their livelihoods.

The goods have included hard and soft drugs and weapons, the more sophisticated smugglers equipped with off-road vehicles and night-vision binoculars.

Since 2005, the smuggling routes have also served to bring more than 50,000 African asylum-seekers and economic migrants to Israel. The Israeli government originally conceived of the new border fence as a means to stem the flow.

But Israel says that the smuggling routes are increasingly serving as an infrastructure for terrorism. And in this craggy terrain, identities are easily obfuscated and confused. Israeli military officers in the area say that it is still not known whether the actual perpetrators of the attack last August were Palestinians, Bedouins or fugitives of the Egyptian government.

The fence, now half complete, is only part of a system designed to secure the border that includes new fortifications and advanced technological surveillance tools.

The military also relies on traditional methods, with an army unit of mostly Bedouin trackers scouring constantly smoothed sand paths running parallel to the border for signs of infiltration.

The smugglers use low-tech methods in trying to cover their tracks, for example by laying mats or wooden planks across the sand paths, crossing them in sheepskin shoes or in shoes with the soles stuck on backward to make it look as if they were heading for Egypt.

The trackers’ knowledge is passed from father to son, and it takes the trained eye and desert sensibility of a Bedouin tracker to spot the traces left behind by the Bedouin smugglers.

Asked how the trackers felt about revealing the tracks of other Bedouin, the Bedouin commander of the tracking unit in the area shrugged and replied, “Everybody has their job.”