JERUSALEM (AP) — Palestinian militants in the Hamas-ruled Gaza Strip fired rockets and mortars into southern Israel early Monday, despite an unofficial truce meant to defuse days of escalating violence.

Around midday, a group that had held out from joining the cease-fire announced it would comply.

The Israeli military said 15 projectiles were launched at Israel overnight, most of which fell in open fields. No injuries were reported. Israel retaliated with an airstrike before midnight Sunday that targeted a rocket-launching device.

A Hamas official said Sunday that militant groups in Gaza had agreed a truce would go into effect that evening to end three days of clashes between Israel and Gaza gunmen. Hamas security personnel would enforce the Egypt-brokered agreement, he said.

The latest round of violence began with a deadly attack on Israelis near the Egypt-Israel border on Thursday. That touched off a deadly round of Israeli airstrikes and rocket fire from Gaza.

About 15 Palestinians, most of them gunmen, were killed in the air attacks. Eight Israelis died in the border attack and another was killed by rocket fire.

The Popular Resistance Committees had resisted joining the cease-fire because Israel assassinated several of its senior members in an airstrike Thursday, accusing them of involvement in the border ambush, another Hamas official said Monday. He spoke on condition of anonymity because he wasn’t authorized to speak for the other group.

But Monday afternoon, the PRC told a news conference it would join the truce.

In the meantime, militant leaders in Gaza said they were lying low and not answering their telephones, fearing the Israelis would be able to locate and assassinate them.

The sudden flare-up in violence also caused new friction in relations between Israel and Egypt, after Egypt accused Israel of killing five of its security forces while pursuing militants responsible for the frontier ambush on Thursday.

Under pressure from popular anti-Israel sentiment, the Egyptian government at one point threatened to recall its ambassador to Israel. Israel apologized and Egypt recanted.