One Israeli airstrike killed two Hamas militants and another unidentified man, while another flattened a five-story building in northern Gaza, killing at least seven people, including an infant, Hamas officials said.
Israeli aircraft struck more than 30 targets before dawn, and there were constant explosions after first light.
By afternoon, 23 Palestinians had been killed, pushing the death toll to 777 in the two-week-old conflict, according to Gaza health officials who say at least half of those killed were civilians. Thirteen Israelis have also been killed.
The United Nations kept aid deliveries to Gaza on hold for a second day because of security concerns, but Palestinians who risked going to relief centers could still get food and medicine, just over half the territory's population of 1.4 million relies on the U.N. for food.
U.N. officials said later they planned to resume the aid operations "as soon as practical," based on assurances from the Israeli military that aid workers would be better protected. The U.N. halted deliveries Thursday after Israeli tank fire killed an aid truck driver and the Red Cross restricted its activities after one of its drivers was injured in a similar incident.
The World Food Program and UNICEF stressed they were still operating in the Palestinian territory, where 1 million people were without electricity and 750,000 didn't have without running water, according to the United Nations.
Despite harsh criticism from international aid groups, Israel has said it is doing everything it can to facilitate humanitarian work, citing the three-hour pauses in fighting it agreed to during the last three days, including Friday. Humanitarian workers say the lulls are inadequate.
A U.N. Security Council resolution approved Thursday night called urgently for an immediate, durable and fully respected cease-fire, leading to the full withdrawal of Israeli forces from Gaza. The U.S., Israel's closest ally and a veto-wielding member of the Security Council, abstained.
While the call is tantamount to a demand on the parties, Israel's troops won't be required to pull out of Gaza until there is a durable cease-fire.
The resolution calls on U.N. member states to intensify efforts to provide guarantees in Gaza to sustain a lasting truce, including prevention of illicit trafficking in arms and ammunition.
In Israel's first official response to the resolution, Prime Minister Ehud Olmert's office said the Hamas rockets fired at Israel Friday "only prove that the U.N.'s decision is not practical and will not be kept in practice by the Palestinian murder organizations."
A Hamas spokesman said the Islamic militant group "is not interested" in the cease-fire because it was not consulted and the resolution did not meet its minimum demands.
Israel launched its assault on Dec. 27 in an attempt to halt years of rocket fire from the Hamas-controlled territory.
Despite the devastating offensive, Hamas kept up rocket attacks on southern Israel. More than 30 rockets hit Friday in and around two of the largest southern cities, Beersheba and Ashkelon. No casualties were reported.
A day after two people suffered light injuries in northern Israel when at least three rockets were fired from southern Lebanon, the Lebanese army said its soldiers had found 34 missiles in two caches near the border.
In Geneva, the U.N. High Commissioner for Human Rights called for an independent war crimes investigation in Gaza after reports that Israeli forces shelled a house full of Palestinian civilians, killing 30 people.
Navi Pillay told an emergency meeting of the U.N. Human Rights Council that the harm to Israeli civilians caused by Hamas rockets was unacceptable, but did not excuse any abuses carried out by Israeli forces in response.
Israeli military spokeswoman Avital Leibovich cited alleged inaccuracies in the U.N. report and said it had not been confirmed.
"We don't warn people to go to other buildings, this is not something we do," she said. "We don't know this case; we don't know that we attacked it."
Secretary of State Condoleezza Rice said the U.S. "fully supports" the Security Council resolution but abstained "to see the outcomes of the Egyptian mediation" with Israel and Hamas, also aimed at achieving a cease-fire.
Osama Hamdan, a Hamas envoy to Lebanon, told the al-Arabiya satellite channel that the group "is not interested in it because it does not meet the demands of the movement."
Hamas spokesman Sami Abu Zuhri said the U.N. failed to consider the interests of the Palestinian people.
"This resolution doesn't mean that the war is over," he told the Al-Jazeera satellite television network. "We call on the Palestinian fighters to mobilize and be ready to face the offensive, and we urge the Arab masses to carry on with their angry protests."
Israel's government says any cease-fire must guarantee an end to rocket fire and arms smuggling into Gaza. During a six-month cease-fire that ended with the current operation, Hamas is thought to have used tunnels under the Egypt-Gaza border to smuggle in the medium-range rockets it is now using to hit deeper than ever inside Israel.
Hamas has said it won't accept any agreement that does not include the full opening Gaza's blockaded border crossings. Israel is unlikely to agree to that demand, as it would allow Hamas to strengthen its hold on the territory which it violently seized in June 2007.
German Foreign Minister Frank-Walter Steinmeier was heading to the Middle East on Friday in support of international attempts to reach a lasting cease-fire in Gaza. Spain said its foreign minister, Miguel Angel Moratinos, also planned to visit the region beginning Monday.
With Israeli troops now in control of many of the open areas used by militants to launch rockets, gunmen have continued shooting from inside populated neighborhoods.
The military said its forces targeted weapons caches, rocket-launching pads and rocket squads Friday.
Fares Alwan, 49, said he was eating with his family when their house came under fire.
"I took my kids and wife and started running away for cover," Alwan said. "We saw wounded people in the street while we were running."
Israeli gunboats also shelled Gaza City, and one shell landed in the city center. One person was killed and three were injured, Palestinian medical officials said.
The conflict has left hundreds of thousands of Palestinians in Gaza increasingly desperate for food, water, fuel and medical assistance, and the situation was expected to worsen as humanitarian efforts fall victim to the fighting.
One of the dead Thursdays was a Ukrainian woman, the first foreigner to die in the fighting, according to Gaza Health Ministry official Dr. Moaiya Hassanain. He said the woman was married to a Palestinian doctor who trained in Ukraine and returned with her to Gaza. Her 2-year-old son was also killed in the tank shelling east of Gaza City, he said.
Israeli police said a Palestinian man armed with an ax chased after people in the central Israeli town of Rehovot on Friday, slightly injuring at least one person. Police spokesman Micky Rosenfeld said police officers subdued the man and were questioning him.
The West Bank saw its biggest protests so far, as at least 2,000 people took to the streets following Friday prayers to express their anger at the Israeli offensive.
Hamas says Abbas' term officially ended Friday, but Fatah says he will remain president until new elections are held.
Tens of thousands of people condemned Israel's offensive at protest rallies in Egypt, Jordan, Iraq and Qatar. Protesters also took to the streets outside the Middle East, in Algeria, Greece, Turkey, Kenya, Malaysia, the Netherlands and Bulgaria.
The Libyan state news agency reported that President Moammar Gadhafi has called on Arabs to allow volunteers to fight the Israelis in Gaza. The one-sentence call was posted on Libya's JANA news agency.