AP

By AMY TEIBEL

JERUSALEM (AP) - Militants crossed from Egypt's turbulent Sinai Peninsula into southern Israel on Monday and opened fire on civilians building a border security fence, defense officials said. One of the Israeli workers was killed, and two assailants died in a gunbattle with Israeli troops responding to the attack.

No group claimed responsibility for the attack, which underscored the growing lawlessness in the Sinai desert since longtime Egyptian President Hosni Mubarak was toppled by a popular uprising last year.

Military spokeswoman Lt. Col Avital Leibovich said the assailants have not been identified but acknowledged that defense officials suspected Palestinian militants in the Hamas-run Gaza Strip, which also borders the Sinai desert in that same area, might have been involved.

Several hours after the attack, an Israeli airstrike killed two men riding a motorcycle in the northern Gaza Strip near the Israeli border. The Islamic Jihad militant group said the men were members on a "reconnaissance" mission and vowed revenge. Military officials said the incident was not connected to the earlier infiltration from Egypt.

Israeli security officials have grown increasingly anxious about the security situation in the Sinai since Mubarak's ouster. Continued political turmoil in Egypt, weak policing in the Sinai and tough terrain have all encouraged Islamic militant activity in the area. The mountainous desert now harbors an array of militant groups, including Palestinian extremists and al-Qaida-inspired jihadists, Egyptian and Israeli security officials say. The tumultuous situation surrounding Egyptian elections, in which Islamic groups made a strong showing, has added to Israeli unease.

Israeli Defense Minister Ehud Barak told Army Radio that there has been "a worrisome deterioration of Egyptian control" over the Sinai. Barak said he expected the winner of this week's presidential elections in Egypt to honor the country's international obligations - an apparent reference to Egypt's 1979 peace treaty with Israel. The Muslim Brotherhood has said it would respect the historic peace accord but that it would also seek modifications.

Vice Premier Shaul Mofaz, a former defense minister and military chief, said he hoped Israel could conduct a security dialogue with the Egyptians and demand more forceful policing in the Sinai.

"No doubt Sinai has become a security problem," Mofaz told Army Radio. "Today's incident ratchets it up a notch."

There was no immediate comment from Egypt on the attack.

Following Mubarak's ouster, Israel stepped up construction of a security fence across the 230-kilometer (150-mile) border with Egypt in a bid to keep out both militants and illegal migrants from Africa. The government has said it expects the fence to be completed by the end of the year.

In Monday's attack, two civilian vehicles carrying construction workers were driving toward the security fence when militants activated a roadside bomb and opened light arms and anti-tank fire at them, said Leibovich, the military spokeswoman.

One of the vehicles was struck and turned over into a nearby ditch, killing one worker, she said. Israeli troops rushed to the area and engaged in a gunbattle with the militants. One militant, who was carrying a large explosive device, blew up, she said. Another militant, and possibly two others, also died, but other gunmen may have escaped back into Egypt, she said.

The militants were carrying camouflage uniforms, flak jackets, helmets and assault rifles, she said. There was no word on their identities or membership in any of a wide range of armed groups.

Leibovich said Israelis living in five small communities in the area were instructed to lock themselves inside their homes, and two major southern roads were closed to civilian traffic while troops scoured the area for other militants. The military later concluded no other gunmen were in the area.

Israel had been bracing for the possibility of more attacks from the Sinai after two rockets believed fired from there struck southern Israel over the weekend, though Leibovich said it was unclear whether the two events were related.

The magnitude of the growing threat from Sinai was driven home last August, when gunmen from Sinai infiltrated Israel and ambushed vehicles on a desert highway, killing eight Israelis. Six Egyptians were killed in Israel's subsequent hunt for the militants, causing a diplomatic crisis between the two neighbors that ended with an Israeli apology.

The deadly August attack shattered decades of calm along the frontier area, prompting officials on both sides of the border to examine security arrangements and pushing Israel to speed up construction of the border fence.

As part of its landmark first peace treaty with an Arab state, Israel agreed in 1979 to return the Sinai, captured in the 1967 Mideast war, to Egypt, but insisted the vast desert triangle separating Asia from Africa be significantly demilitarized. As the frontier area grew more volatile following Mubarak's ouster, Israel allowed thousands more Egyptian troops to police the area and has beefed up its own military deployment along the border.

The reinforced security deployment has not quieted the Sinai, however, and democratic elections for parliament and president did not resolve the instability in Egypt, which has Israel worried about the future of the 1979 peace accord.

The ruling Egyptian military dissolved the newly elected parliament and assumed sweeping powers subordinating the president and ensuring their hold on the state. The Muslim Brotherhood, which declared early Monday that its candidate, Mohammed Morsi, won this week's presidential election, has challenged the military's power grab, raising the prospect of a power struggle between Egypt's two strongest forces.