JERUSALEM — Israel sealed all border crossings with the Gaza Strip today, cutting off the flow of vital supplies to the besieged territory in an attempt to stop Palestinian Arab rocket barrages on Israeli border towns.

But violence continued today, with Israeli air strikes killing two civilians and one militant while Palestinian Arabs fired 16 rockets into southern Israel, including one that damaged a day care center.

The bloodshed clouded American-backed peace talks that Israel and the government of Palestinian Authority president, Mahmoud Abbas, renewed last month. The Gaza quagmire could complicate President Bush’s efforts to prod the sides toward a final peace deal by the end of the year.

A U.N. agency warned that the Israeli closure of the Gaza passages would increase hardship in the impoverished territory of 1.4 million Palestinian Arabs. Hamas threatened suicide attacks on Israel if its sanctions and military raids continued.

“If the bloodshed in Gaza and the West Bank does not stop, there will be similar bloodshed in … Tel Aviv,” a Hamas spokesman, Hamad al-Rukeb, said in a statement.

The last suicide attack claimed by Hamas was in August 2005, when a bomber blew himself up and severely wounded two security guards outside the bus station in the southern city of Beersheba. The last Hamas bombing to claim Israeli lives was in the same city a year earlier, when two bombers on separate city buses exploded, killing 16 people.

Gaza militants intensified rocket barrages after an Israeli anti-rocket raid in Gaza on Tuesday killed 19 Palestinian Arabs, including the militant son of a prominent Hamas leader.

Israeli aircraft staged more strikes today, pounding the derelict local offices of the Hamas-run interior ministry in Gaza City. The building, in the heart of a residential neighborhood, had been vacant since it was severely damaged in a July 2006 air strike. Hospital officials said a woman was killed and at least 46 other civilians were injured by flying debris and shrapnel.

An Israeli military spokeswoman said the strike against what she called “a Hamas headquarters” was part of Israel’s campaign against the rocket fire.

Planes also attacked a rocket launch squad in the northern Gaza Strip — killing a militant and a civilian bystander, Hamas said — and a disused central Gaza base of Hamas security forces, where there were no casualties.

Defense Minister Ehud Barak’s decision to close the Gaza crossings — conduit for vital food and humanitarian supplies from Israel and aid organizations — is meant to pressure the Hamas rulers of Gaza to halt rocket fire, a ministry spokesman, Shlomo Dror, said.

“It’s time that Hamas decide to either fight or take care of its population,” Mr. Dror said. “It’s unacceptable that people in (the southern Israeli town of) Sderot are living in fear every day and people in the Gaza Strip are living life as usual.”

Since Hamas took over Gaza, Israel has cut off all ties with the territory, only allowing in food, fuel, and humanitarian supplies. On several occasions in recent months, Israel has reduced fuel and electricity supplies with the hope that Gaza’s population would pressure the militants to stop the rocket fire.

Since the siege was imposed, Palestinian Arabs in the Gaza Strip have had to live with erratic supplies of food and no imports of products like spare car parts and computer paper.

“This can only lead to the deterioration of an already dire situation,” a spokesman for the U.N. agency in charge of Palestinian Arab refugees, Christopher Gunness, said of the latest Israeli decision.

A Palestinian Arab negotiator, Saeb Erekat, said the Israeli decision would not bring a cessation of the rocket fire.

“Violence and military solutions and collective punishment will breed violence and more hatred … and it will not provide no peace and security,” Mr. Erekat said.

Mr. Abbas’s spokesman, Nabil Abu Rdeineh, said Palestinian Arab negotiators have urged America to stop Israel from “sabotaging” the talks.

The leading official of the U.N. agency in charge of Palestinian Arab refugees, John Ging, said Israel notified his office that the crossings would be closed for “several days.” On a regularly working day an average of 120 trucks of food and humanitarian supplies enter Gaza, Mr. Ging said.

Mr. Dror said that Gazans had enough food so that no one would go hungry.

“There is a government decision that there will not be a humanitarian crisis in Gaza,” Mr. Dror said.

Israeli officials will reevaluate the situation next week and decide whether to reopen the passages, he said.

At least 30 Palestinian Arabs have been killed since the violence escalated Tuesday, most of them armed militants.

Hamas and other groups have fired more than 150 rockets and mortars since Tuesday, according to the Israeli military. The strikes caused no serious injuries, although 12 Israelis have been killed by the rockets in the past six years.