Jersualem ? Israel implemented a unilateral cease-fire early today in its 22-day offensive that turned Gaza neighborhoods into battlegrounds and dealt a stinging blow to the Islamic militants of Hamas. But Israeli troops will stay in the Palestinian territory for now and Hamas threatened to keep fighting until they leave.

In announcing the cease-fire late Saturday, Prime Minister Ehud Olmert said Israel had achieved its goals and more.

“Hamas was hit hard, in its military arms and in its government institutions. Its leaders are in hiding and many of its men have been killed,” Olmert said.

Israel launched the offensive on Dec. 27 to stop years of rocket fire from Gaza at southern Israeli towns. But the rockets did not stop coming throughout the assault. Militants fired about 30 rockets into Israel on Saturday, eight of them around the time Olmert spoke.

More than 1,100 Palestinians have been killed in the offensive, about half of them civilians, according to Palestinian and U.N. officials. At least 13 Israelis have also been killed.

According to Olmert’s statement, the cease-fire went into effect at 2 a.m. local time (6 p.m. CST). The military warned in a statement early Sunday that attacks on soldiers or civilians “will be met with a harsh response.”

If Hamas holds its fire, the military “will weigh pulling out of Gaza at a time that befits us,” Olmert said. If not, Israel “will continue to act to defend our residents.”

Israel’s insistence on keeping troops in Gaza raises the specter of a stalemate with Hamas, which has insisted that it will not respect any cease-fire until Israel pulls out of the territory, with a population of 1.4 million.

Hamas spokesman Fawzi Barhoum in Gaza said a unilateral cease-fire was not enough to end Hamas’ resistance — echoing the stance taken earlier by Hamas leaders in exile.

“The occupier must halt his fire immediately and withdraw from our land and lift his blockade and open all crossings and we will not accept any one Zionist soldier on our land, regardless of the price that it costs,” Barhoum said.

Offensive could be renewed

In the hours leading up to the vote by the 12-member Security Cabinet, and even as they met, Israel kept bombarding Gaza.

Earlier Saturday in the northern town of Beit Lahiya, Israeli shells struck a U.N. school where 1,600 people had sought shelter. One shell scored a direct hit on the top floor of the three-story building, killing two boys, U.N. officials said.

Gaza militants launched eight rockets into Israel around the time Olmert announced the cease-fire, the Israeli military said. There were no reports of casualties. Five long-range Grad rockets exploded near the city of Beersheba in the hour after Olmert’s televised address, Israel Radio reported.

Foreign Minister Tzipi Livni indicated that Israel would renew its offensive if Hamas militants continued to fire rockets at Israel.

“This campaign is not a one-time event,” she said in an interview with the Israeli YNet news Web site. “The test will be the day after. That is the test of deterrence.”

Palestinians reacted with skepticism and called on world leaders attending a summit planned for today in Egypt to put pressure on Israel to withdraw immediately.

“We had hoped that the Israeli announcement would be matched by total cessation of hostilities and the immediate withdrawal of Israeli forces from Gaza,” said Saeb Erekat, a top aide to Palestinian President Mahmoud Abbas, a Hamas rival. “I am afraid that the presence of the Israeli forces in Gaza means that the cease fire will not stand.”

Summit today

The cease-fire vote comes just days ahead of Barack Obama’s inauguration as president on Tuesday. Outgoing Secretary of State Condoleezza Rice said the Bush administration welcomed Israel’s decision and said the ultimate goal remains a lasting truce that is fully respected and will return peace to Gaza.

The summit set for today in Egypt is meant to give international backing to the cease-fire. Leaders of Germany, France, Spain, Britain, Italy, Turkey and the Czech Republic — which holds the rotating EU presidency — are expected to attend along with Palestinian President Mahmoud Abbas, Egyptian President Hosni Mubarak and U.N. Secretary-General Ban Ki-moon.

It was not immediately clear whether Israel would send a representative, and Hamas has not been invited.

Ban welcomed Israel’s move and called on Hamas to stop its rocket fire. He said “urgent humanitarian access for the people of Gaza is the immediate priority,” and “the United Nations is ready to act.”