At least 15 people were killed and another 150 people wounded in an Israeli air strike on a market near Gaza City, medics said.
Emergency services spokesman Ashraf al-Qudra said the strike hit a busy market in the battered Shejaiya neighbourhood, which lies between Gaza City and the Israeli border.
The strike came shortly after the Israeli army said it was observing a humanitarian lull that would be in force for four hours from 1200 GMT.
But it said the lull would not apply in areas where troops were "currently operating" in a move denounced as a publicity stunt by Hamas.