Two people were lightly injured, and the rockets on Israel's north raised the specter of renewed hostilities with Hezbollah, just 2 1/2 years after Israel battled the guerrilla group to a 34-day stalemate. Hezbollah started the 2006 war as Israel was battling Palestinian militants in Gaza.
Lebanon's government, wary of conflict, quickly condemned the rocket fire and said it was trying to determine who was behind the attack. Israel fired mortar shells into southern Lebanon in response.
In new Gaza fighting, Israel killed at five people, including four militants, raising the death toll from its 13-day offensive to nearly 700, according to Palestinian medical officials. With roughly half the dead believed to be civilians, international efforts to broker a cease-fire have been gaining steam.
Later Thursday, Israel said it would halt military action for three hours to allow Gaza residents to stock up on supplies. The lull would enable humanitarian groups to do their work, and Israel would send aid and fuel into the territory, said Israeli military official Peter Lerner.
One of the Lebanese rockets went through the roof of a retirement home in Nahariya, about five miles from the border, and exploded in the kitchen as some 25 residents were eating breakfast in the adjacent dining hall. One resident suffered a broken leg, another bruises, apparently from slipping on the floor after emergency sprinklers came on.
"The rocket entered through the roof, hurling the water heaters into the air. It went through bedrooms upstairs and then into the kitchen. There was a serious blast," said Henry Carmelli, the home's manager.
About three hours later, air-raid sirens went off again. Residents in two northern towns reported explosions of incoming rockets, though some reports suggested there had been a false alarm. Police said they were searching for the fallen projectiles.
Israel has repeatedly said it was prepared for a possible attack on the north since it launched its bruising campaign against Hamas militants in Gaza on Dec. 27. Israel has mobilized thousands of reserve troops for such a scenario, and leaders have warned Hezbollah of dire consequences if it enters the fighting.
There was no immediate claim of responsibility for the rocket attacks. Lebanese Prime Minister Fuad Saniora condemned both the attacks and Israel's retaliatory fire, saying the attackers were trying to undermine stability.
Hezbollah, which did not comment, has said it does not want to draw Lebanon into a new war. Small Palestinian groups, who have rocketed Israel twice since the end of the 2006 war, have recently threatened to open a new front against Israel if the fighting in Gaza continued.
"Even though we have the ability to respond with great force, the response needs to be carefully considered and responsible," Sheetrit told Army Radio. "We don't need to play into their hands."
Shortly after the first rockets fell around the town of Nahariya, five miles south of the Lebanese border, Lebanese TV stations reported Israeli mortar fire on open areas in southern Lebanon. The Israeli military confirmed it carried out "pinpoint fire" in response without elaborating.
Israeli defense commentators said they expected the incident to be a one-time show of solidarity with the Palestinians, not a declaration of war. Still, police said public bomb shelters throughout the north were opened.
Earlier, Palestinians reported some two dozen airstrikes around Gaza City before dawn. One militant was killed and 10 wounded.
An airstrike in northern Gaza killed three members of a rocket-launching cell, Palestinian medical officials said. The attack took place about 150 yards from a hospital and wounded 12 bystanders. The Israeli army has repeatedly said militants use civilian areas for cover.
Also, there were clashes between Israeli armored forces and Hamas militants in southern Gaza.
Israel had resumed its Gaza offensive Wednesday after a three-hour lull to allow in humanitarian aid, bombing heavily around suspected smuggling tunnels near the border with Egypt after Hamas responded with a rocket barrage. Israeli planes destroyed at least 16 empty houses.
The tunnels are Hamas' lifeline, used to bring in arms, money and basic goods. Israel says local homes are used to conceal the tunnels.
Israeli warplanes bombed the border area after leaflets were dropped warning residents to leave. More than 5,000 people fled to two U.N. schools turned into temporary shelters.
While the U.N. Security Council failed to reach agreement on a cease-fire resolution, Egypt's U.N. Ambassador Maged Abdelaziz said representatives of Israel, Hamas and the Palestinian Authority agreed to meet separately with Egyptian officials in Cairo.
Senior envoy Amos Gilad arrived in Egypt Thursday morning.
The latest casualties brought the total Palestinian death toll during Israel's assault to 692 — including some 350 civilians, among them 130 children - according to Palestinian health officials, and drove home the complexities of finding a diplomatic solution for Israel's Gaza invasion. Ten Israelis have been killed, including three civilians, since the offensive began.
In Turkey, a Mideast diplomat who spoke on condition of anonymity because he was not authorized to speak publicly said that country would be asked to put together an international force that could help keep the peace. And diplomats in New York worked on a U.N. Security Council statement backing the cease-fire initiative but failed to reach agreement on action to end the violence.
For Israel to accept a proposed cease-fire deal, "there has to be a total and complete cessation of all hostile fire from Gaza into Israel, and ... we have to see an arms embargo on Hamas that will receive international support," said government spokesman Mark Regev.
For its part, Hamas said it would not accept a truce deal unless it includes an end to the Israeli blockade of Gaza — something Israel says it is not willing to do. Israel and Egypt have maintained a stiff economic embargo on Gaza since the Hamas takeover.
The Palestinian Authority controls the West Bank while Hamas rules Gaza — two territories on opposite sides of Israel that are supposed to make up a future Palestinian state. Hamas took control of Gaza from forces loyal to Palestinian Authority President Mahmoud Abbas in June 2007.
Growing international outrage over the human toll of Israel's offensive, which includes 3,000 Palestinians wounded — could work against continued fighting. So could President Bush's departure from office this month and a Feb. 10 election in Israel.
But Israel has a big interest in inflicting as much damage as possible on Hamas, both to stop militant rocket fire on southern Israeli towns and to diminish the group's ability to play a spoiler role in peace talks with Palestinian moderates.
The Israeli Cabinet formally decided on Wednesday to push ahead with the offensive while at the same time pursuing the cease-fire.
The military has called up thousands of reserve troops that it could use to expand the Gaza offensive. Defense officials said the troops could be ready for action by Friday.
In Geneva, the international Red Cross said it found four small children alive next to their mothers' bodies in the rubble of a Gaza home hit by Israeli shelling. The neutral aid group says a total of 15 dead were recovered from two houses in the Zaytun neighborhood of Gaza City on Wednesday.
A Red Cross spokesman said rescuers had been refused permission by Israeli forces to reach the site for four days. It said the delay in allowing rescue services access was "unacceptable."