Israeli air strikes and artillery fire killed 10 Palestinians on Friday, including seven people on a crowded Gaza beach, the highest Palestinian death toll in a single day since December 2004, Palestinian officials said.

Among those killed on the beach were three children, including an infant, a 3-year-old and a 10-year-old, who were playing at the time, witnesses said.

About 20 people were injured by the shelling, which Palestinian sources said came from Israeli ships. Palestinian President Mahmoud Abbas called it "a bloody massacre".

The Israeli army initially said its ships had fired shells at militants who launched rockets against the Jewish state after Israel's killing of a top militant who also served as a senior security chief appointed by the Hamas-led government.

But army spokesman Jacob Dallal said later that the shells were neither fired by Israeli naval ships nor the air force. "We are checking if it was artillery," he said.

Army chief Dan Halutz ordered an investigation into the deaths on the beach and halted the shelling, Dallal said.

Dallal said the army does not know "for certainty" if the shells were fired by Israel, and he said the military "deeply regretted" any civilian deaths.

What a load of crap. How can you 'halt the shelling,' yet not know 'for certain' if Israelis fired the shells?

Palestinians can't even let their children enjoy the few beaches they have access to without fear of them being killed by Israeli fire. Abominable.