A deadly cross-border attack on Monday, alongside the self-declared victory of the Muslim Brotherhood in Egypt's presidential elections, have sparked new concerns in Israel over the security of its western border and the future of relations with Cairo.

One Israeli was killed in a combined shooting and bombing attack carried out by three heavily-armed militants who crossed into Israel from the Sinai Peninsula, some 30 km south of Gaza, and ambushed vehicles carrying private contractors headed for work on a border fence being built in the area.

An infantry unit, which arrived at the scene moments later, identified and engaged the militants, killing two, the army said. Two tanks deployed to the area to assist efforts to thwart additional attacks, but were withdrawn shortly later.

While there was no official claim of responsibility for the attack, unnamed Israeli political sources laid the blame on Egypt' s ambiguous political future.

"The Sinai has turned into Afghanistan, a no man's land," the Israeli Yedioth Ahronoth daily quoted the sources as saying. "The Egyptians themselves don't have the strength to control what is happening there; our feeling is one of helplessness, that this thing may blow up in our faces."

Describing the border attack as "a worrisome escalation," the sources further said that the "critical question is how determined Egypt's next president will be to enforce law and order in Sinai, especially at the border."

"This determination, or its absence, will have decisive influence on the future of bilateral relations between Israel and Egypt," they said.

Concerning previous statements by Muslim Brotherhood candidate Mohammed Morsy that Egypt under his leadership would uphold international agreements signed by Hosni Mubarak's regime but would "reexamine" relations with Israel, the sources estimated that Cairo would remain committed to the 1979 peace treaty.

The United States is "intensively involved" in Egypt, the sources noted, which means that an Islamist regime would not rush to violate the terms of the accords, fearing the loss of U.S. military aid and a confrontation with the international community.

"Even the Islamists known that annulling the peace agreement immediately after rising to power will not be a smart move. We assume that the result will be a cold peace, but that the agreement will be preserved," the sources told Yedioth.

Israeli military officials have also voiced deep concern in the wake of Monday's border attack, which came 72 hours after two Grad- type rockets were fired from Sinai and landed in a region north of the Red Sea port city of Eilat and near the southern Negev town of Mitzphe Ramon - the first time that both these areas were targeted.

"Sinai has become an enclave of terrorism and various elements, including al-Qaida, Hamas and groups affiliated with world Jihad, are active there and are exploiting the leadership vacuum in Egypt, " according to one official who said that preparations were underway to allocate sources, mainly intelligence assets, to the western border.

He said that the security establishment fears that terror groups roaming the Sinai would attempt to drag the Israeli army into a "strategic ambush" with Egypt at a time of rising tensions along the border.

Meanwhile, a new round of violence between Israel and Gaza militants escalated in the past 24 hours, with intermittent rocket fire by militants followed by Israeli air strikes.

In a rare move, the military wing of Hamas claimed responsibility for firing four rockets into southern Israel overnight Monday, which exploded in open areas and caused no casualties or damage. Officials here said the attack was highly unusual for Hamas, which has avoided lobbing rockets toward Israel for many months.

Prior to that attack, Israeli aircraft carried out several strikes against militant sites and rocket launching squads throughout the coastal enclave in which four Palestinians were killed and five others were wounded, according to Palestinian medical sources.

In the most recent strike, aircraft hit militants planting explosives near the border with central Gaza, while earlier strikes targeted Islamic Jihad operatives.

The Israeli army said it is maintaining high alert along the border in expectation of terrorist retaliation.