Israeli forces have killed at least twelve Palestinians, including a 12 year-old boy, after two detachments of Israeli tanks and troops forced their way into northern and southern Gaza, exchanging fire with Palestinian fghters.
Israeli fire struck a Gaza City house, killing four people, including a 12-year-old boy, medics said.
Five Palestinian fighters were killed in fighting with the Israelis in another outlying part of the city, it was reported.
In southern Gaza, an Islamic Jihad militant was killed in a clash with troops in the town of Khan Younis. Hospital officials said a total of 40 people were wounded by Israeli shells in Gaza City.
Two more Palestinians died in other violence. In Khan Younis, a Hamas militant was killed while mishandling explosives, and a senior Islamic Jihad member was killed in what Palestinians said was an airstrike. Israel, which usually acknowledges airstrikes, denied involvement.
The army said two soldiers were wounded when their tank was hit by a shoulder-launched rocket.
Palestinians fired a rocket into Israel, but it struck open ground near the Gaza border, causing no casualties, the army said. Several mortar shells were also fired at Israel but fell short, landing on the Gaza side, the military said.
A 12-year-old lay in the street, his arms twisted at odd angles, near a house in a Gaza City neighbourhood where residents and medical workers said a shell fired by an Israeli tank exploded.
He was pronounced dead in a hospital along with two men, their bodies shredded by shrapnel. Residents said the men were civilians.
A military spokesman in Tel Aviv said a tank shell fired in Gaza City's Shejaia neighbourhood was aimed at a gunman, and he had no information about a house being hit. Residents said tanks in the area later withdrew towards the Israeli frontier.
The death toll is the highest in a single day since Hamas seized control of Gaza two weeks ago after routing the Fatah forces. The takeover has left the Palestinians with a Hamas government in Gaza and a Fatah government in the West Bank.
Representatives of the Quartet of Middle East mediators - the United States, the European Union, Russia and the United Nations - met in Jerusalem on Tuesday for talks aimed at boosting progress in talks between Israel and the Palestinian Authority following Hamas's Gaza takeover.
The United States and Israel want to isolate Hamas in Gaza while bolstering Abbas and an emergency government he formed in the occupied West Bank after dismissing a unity cabinet led by Hamas.
A US official in Washington said the Quartet was expected to name outgoing British Prime Minister Tony Blair as their Middle East envoy later in the day, after he steps down.