TEL AVIV—A deadly string of attacks erupted along Israel´s southern border on Monday, leaving at least seven dead and highlighting the strains on the country´s ties with Egypt during Cairo´s rocky political transition.

In an early-morning ambush, a team of gunmen from Egypt´s Sinai Peninsula snuck into Israel and attacked defense-ministry vehicles with building contractors overseeing the construction of a border barrier meant to prevent just such an infiltration. No one claimed responsibility.

Israeli soldiers killed two of the infiltrators, and troops carried out a several-hour manhunt along the border in search of more militants. Israel´s army called tanks to a partially demilitarized border area to bolster the response, a rare move given the peace treaty with Egypt, which permits only infantry to be stationed in the border zone.

Hours later, Israeli aircraft targeted a squad of Palestinian snipers in the northern Gaza Strip, killing two Islamic Jihad members. An Israeli military spokesman said the strikes were unrelated to the Sinai incident.

There was no immediate response from the Palestinian Authority. The Islamic Jihad said the men were members on a "reconnaissance" mission and vowed revenge.

The day of violence came just days after two Grad Katyusha rockets were fired from Sinai at areas in southern Israel with military bases. The liberal Ha´aretz newspaper reported Sunday the attack had been ordered by the Egyptian Muslim Brotherhood via Hamas. A senior Israeli defense official, Amos Gilad, dismissed the report.

Israeli military officials have said in private they understand that Egypt´s military rulers have been focused on domestic politics rather than tightening control over the vast Sinai Desert. Still, an upsurge in attacks underscored the potential for the security vacuum to destabilize relations.

In Egypt, the Muslim Brotherhood claimed victory for its candidate, Mohammed Morsi, in the elections that ended Sunday.

"We see here a disturbing deterioration in Egyptian control in the Sinai," said Defense Minister Ehud Barak in a statement. "We are waiting for the results of the election. Whoever wins, we expect them to take responsibility for all of Egypt´s international commitments, including the peace treaty with Israel, and the security arrangements in the Sinai; [and] swiftly putting an end to these attacks."

In Washington, State Department spokeswoman Victoria Nuland said the U.S. condemned the "terrorist attacks on civilians in Israel from the Sinai" and encouraged "the Egyptian government to find a lasting resolution to the issue of Sinai security."

Egypt´s ruling military generals didn´t comment publicly on the incidents.

The Monday attack was the worst attack since August, when a group of infiltrators killed eight Israelis, touching off a cross-border fight that left several Egyptian soldiers dead. That flare-up touched off riots in Egypt at the Israeli Embassy that required the intervention of the U.S. to prevent the harming of Israeli security guards.

Despite widespread anxiety in Israel about the growing political uncertainty in Egypt, Israeli officials and analysts have predicted that the countries´ three-decade-old peace treaty would survive no matter who emerged victorious in the presidential election. Israeli and Egyptian militaries enjoy a good working rapport.

Nonetheless, some Israeli commentators expressed concern on Monday that bilateral ties might be eroded by the election of an Islamist presidency.

"Regardless of the identity of the victor...it´s clear that Israel should expect more incidents like this," wrote Avi Issacharoff on the online website of the Ha´aretz newspaper. "The chaos in Sinai isn´t expected to disappear in the near future."

The escalation in attacks leaves Israel limited options. The country´s military won´t launch retaliatory cross-border attacks because it would violate its 1979 peace treaty with Egypt.

Instead, Israel has invested tens of millions of dollars to build a fence to plug up the 150 mile open frontier with Egypt. It has also bulked up security patrols along the border.

Corrections & Amplifications

The Monday attack was the worst strike since August, when a group of infiltrators killed eight Israelis. An earlier version of this article mistakenly said that two Israelis had been killed in the August attack. (Copyright © Dow Jones & Company, Inc.) 06/19/12)