A combination of pictures shows Israeli policemen and a soldier detaining an Arab-Israeli after he tried to pass a road block in the Israeli Negev desert on June 18, 2012. Israel was still hunting for up to four gunmen who infiltrated the Egyptian border and staged a deadly ambush. (David Buimovitch/AFP/Getty Images)

Gunmen who crossed into Israel from Egypt’s Sinai Peninsula killed a worker assigned to build a border fence early Monday, and two of the assailants died in a clash with soldiers who responded to the incident, the Israeli army said.

The attack about 20 miles south of the Gaza Strip, near the border community of Nitzana, underscored Israeli concerns about worsening security conditions in Sinai, where government control has weakened since the Egyptian revolution last year.

Israeli Defense Minister Ehud Barak said the incident, along with the firing of two rockets on southern Israel over the weekend, indicates “a disturbing deterioration in Egyptian control of security in the Sinai.”

He said Israel expected the winner of Egypt’s presidential election this past weekend “to take responsibility for all of Egypt’s international commitments, including the peace treaty with Israel and the security arrangements in the Sinai, and to swiftly put an end to these attacks.”

Egyptian Gen. Abdelwahab Mabrouk, the governor of North Sinai, the border province from where the attack was allegedly launched, expressed doubt about the veracity of the reports.

“Sinai is secure and under control on our side,” he said, according to a statement carried by the state-run Middle East News Agency. “Any intruders are arrested immediately.”

According to Lt. Col. Avital Leibovitz, an Israeli army spokeswoman, the incident started about 6 a.m., when three gunmen attacked two vehicles carrying laborers who had arrived to work on the border fence. The gunmen targeted the vehicles with an explosive charge, rifle fire and a rocket-propelled grenade, she said.

Leibovitz said a vehicle hit by the explosive and by the gunfire overturned and went into a ditch, killing one worker, whom news reports identified as an Israeli Arab. The spokeswoman said the other workers were not injured.

Israeli troops on border patrol arrived minutes after the attack and traded fire with the assailants, two of whom were killed when a large quantity of explosives carried by one of them detonated, Leibovitz said. She said a third attacker fled back to the Egyptian side of the border, where other members of the attack squad allegedly remained. No soldiers were hurt.

Israeli farming communities and army bases in the border area were locked down after the attack as troops searched for additional infiltrators. Border roads were closed to civilian traffic.

The workers are employed by one of the companies contracted by the Israeli Defense Ministry to construct the 140-mile-long border barrier of steel mesh and razor wire. The fence is still under construction, and the attackers crossed in an area where the barrier was not complete.

Leibovitz said it was unclear where the attackers — who she said were equipped with helmets, flak jackets, camouflage uniforms, Kalashnikov assault rifles and grenades — had come from. But she said the quality and amount of explosives and combat gear they carried were reminiscent of a deadly cross-border attack in August that Israel blamed on a small militant Palestinian faction in Gaza, the Popular Resistance Committees.

In that attack, gunmen who infiltrated from Sinai attacked motorists on a border road north of the Red Sea resort of Eilat, leaving eight Israelis dead. Israel responded with an airstrike in the Gaza Strip that killed six people, including the leadership of the Popular Resistance Committees.

Israel has since accelerated work on the fence, which was originally planned as an obstacle to thousands of African migrants and asylum seekers who sneak across the border each year.

Despite decades of calm since Israel and Egypt signed a peace treaty in 1979, their desert frontier has become more volatile in recent months, as militants seek to use the Sinai area as a launchpad for cross-border attacks.

On Friday, two rockets that Israeli officials said were fired from Sinai landed in southern Israel. In April, at least one Grad rocket landed in Eilat.

Amos Gilad, a senior Israeli defense official, said in a radio interview that extremist groups inspired by Iran and al-Qaeda were “trying to establish themselves in Sinai in order to undermine the government in Egypt and . . . carry out attacks in Israel in order to complicate relations between Israel and Egypt.”

Lawlessness in Sinai, where local Bedouin tribes have long complained of neglect and repression by the Egyptian authorities, also has increased since the revolution. Gunmen have attacked police posts and repeatedly blown up a natural gas pipeline that supplied Israel under a deal widely criticized in post-revolutionary Egypt. The gas shipments have since been canceled.

Bedouins in the Sinai have kidnapped tourists for use as bargaining chips to get relatives in prison released. Security officials also say arms smugglers have taken advantage of lax security in the area to smuggle weapons from Libya.

Also Monday, an Israeli airstrike killed two Palestinian militants from the Islamic Jihad group as they rode a motorcycle in Beit Hanoun in the northern Gaza Strip, local medical officials said.

A statement by the military said aircraft had targeted a squad of snipers that had fired into Israel recently, including a shooting at an Israeli farmer near the border with Gaza last week.

Staff writer Ernesto Londoño in Cairo contributed to this report.