GAZA CITY, Gaza Strip — Hamas militants bombarded a major southern Israeli city with rocket fire Friday, unleashing their most powerful weapons yet in a week of tit-for-tat fighting that threatens to destroy a five-month-old cease-fire.
Both Israel and Gaza’s Islamic militant Hamas rulers held out hope the calm would be restored, and Israeli leaders decided against any immediate major military action in retaliation.
But the sides also vowed to strike hard at each other if violence persisted.
“If you want to leave the truce, we are ready. And if you want to continue it, then abide by it,” Hamas strongman Mahmoud Zahar said in a Friday sermon.
The truce took effect last June, largely halting a cycle of Palestinian rocket attacks on southern Israel and deadly Israel reprisals.
The cease-fire has mostly held, but began to deteriorate last week after an Israeli military raid on what the army said was a tunnel that militants planned to use for a cross-border raid. Eleven militants have been killed, and Palestinians have fired some 140 rockets and mortars from Gaza at Israel.
Israel also has shut Gaza’s vital border crossings, blocking the entrance of food, humanitarian goods and fuel into the impoverished area.
Friday’s rocket barrage was one of the heaviest yet. Nearly 20 rockets were fired into southern Israel, including four Grad-type Katyushas that landed in Ashkelon, some 17 miles north of Gaza. One woman in the southern Israeli town of Sderot was slightly injured by shrapnel, the army said.
It was the first time that rockets have reached Ashkelon in the current round of fighting.
The foreign-made Katyushas are believed to be smuggled into Gaza and have longer ranges than the crude homemade rockets usually fired by militants. With 120,000 people, Ashkelon is the biggest population center in rocket range, and Israel has responded harshly to past attacks on the coastal city.
But Israeli defense officials said the government had decided against any major military action for the time being unless the situation deteriorated. The officials spoke on condition of anonymity because they were discussing classified information.
The barrage came in response to an earlier Israeli airstrike that wounded two militants as they attempted to fire rockets. Hamas said the longer-range rockets were meant to show Israel what it could expect if the truce collapses.
“We will keep protecting our soldiers and people and keep acting against attempts to interrupt the cease-fire, but if the other side will want or wish to keep the cease-fire alive, we’ll consider it seriously,” Israeli Defense Minister Ehud Barak responded.
Mouin Rabbani, an independent analyst based in Jordan, said Hamas escalated its reaction to send a message to Israel that it cannot break the cease-fire without paying a price.
By sundown, the sides appeared to be pulling back, and the area settled into relative calm.