Twenty-two Palestinians and an Israeli soldier were killed as Israel thrust deep into the Gaza Strip, reoccupying areas evacuated 10 months ago and carrying out a wave of air raids.
The Israeli army created a buffer zone in northern Gaza as it widened its offensive against the Palestinians, upping the pressure on the embattled Hamas-led government to free a captured soldier and stop rocket attacks.
Thursday was the bloodiest day since Israel launched the operation more than a week ago and in response the Hamas government put its security forces on high alert and urged all Palestinians to take up arms against the Israeli military.
One Israeli soldier was shot dead in fighting in the northern Gaza town of Beit Lahiya, a killing claimed by one of the Palestinian militant groups behind last week's abduction of 19-year-old corporal Gilad Shalit.
In the worst incident on Thursday, 11 Palestinians were killed, including two fighters loyal to Hamas, in an Israeli bombardment on Beit Lahiya, one of a series of deadly attacks over the day, medics said.
Bloodstained bodies could be seen huddled together as the wounded frantically carried other victims caked in blood through the streets.
After night fell, Israel launched more air strikes on Beit Lahiya, killing four Palestinians and bringing the overall number of dead Palestinians in Gaza on Thursday to 22, both civilians and militants.