An Israeli airstrike killed a Palestinian militant in the Gaza Strip on Sunday, the latest lethal attack in two days of fighting that have left 10 militants and one Israeli civilian dead.

The cross-border violence was the worst in several months after a relative lull that accompanied a prisoner exchange this month between Israel and Hamas, the militant Islamist group that rules the Gaza Strip.

The Israeli army said more than 40 rockets and mortar rounds had been fired at Israel since Saturday, when an Israeli airstrike in Gaza killed five militants from the Islamic Jihad group. The army said the targeted militants had been preparing to fire long-range rockets into Israel.

Despite efforts by Egypt to broker a cease-fire, which led to several hours of calm Sunday, Israel struck from the air near the southern Gaza Strip town of Rafah at what it said was a squad preparing to fire rockets.

The Democratic Front for the Liberation of Palestine, a small militant group, said the strike hit two of its members, killing one and wounding another.

“There is no cease-fire,” said Israeli Prime Minister Benjamin Netanyahu. “I promise that the other side will pay even heavier prices than it has so far, until it stops firing.”

Islamic Jihad leaders said they would suspend their attacks when the Israeli airstrikes were halted.

A total of nine Islamic Jihad militants were killed in Israeli strikes Saturday, and an Israeli man was killed in the southern coastal city of Ashkelon when his car was peppered with shrapnel. A rocket also hit the port city of Ashdod, damaging homes and setting several cars on fire.

Classes were canceled in schools in Israeli communities within a 25-mile radius of the Gaza Strip because of the rocket threat, including at Ben-Gurion University in Beersheba and several colleges, which were to have begun their academic year Sunday. More than 1 million Israelis live within range of rockets stockpiled by militants in Gaza.

Video footage released by Islamic Jihad showed rockets being fired from a multi-barreled launcher mounted on a truck, the first time such a platform has been seen in use in the Gaza Strip. Israeli officials say Gaza militants have been steadily upgrading their weapons capabilities through arms smuggling into the territory.

Some Israeli analysts said Islamic Jihad appeared to be trying to assert its presence after Hamas had boosted its position through the prisoner swap Oct. 18, in which 447 Palestinians were freed from Israeli jails in return for Gilad Shalit, an Israeli soldier held captive by Hamas for more than five years. An additional 550 prisoners are to be released in several weeks as part of the deal.