At least 15 people have been killed and more than 200 injured when a UN-run school used as a shelter in Gaza was shelled, the Gaza health ministry says.
Hundreds of Palestinians were in the school in Beit Hanoun, fleeing heavy fighting in the area.
It is the fourth time that a UN facility has been hit in Israel’s offensive against Hamas militants.
In the past 16 days of fighting, more than 725 Palestinians and 30 Israelis have been killed, officials say.
Israel launched its military offensive on July 8 with the declared objective of stopping Hamas firing rockets from Gaza.
Earlier on Thursday, UN humanitarian chief Valerie Amos said that it was “vital” to have a ceasefire.
“We have over 118,000 people now who are sheltering in UN schools... people are running out of food. Water is also a serious concern,” she said.
She said the conflict meant 44% of Gaza was a no-go area for Palestinians, and residents were running out of food.
Israeli PM Benjamin Netanyahu said on Thursday he regretted each Palestinian civilian death, but said they were “the responsibility of Hamas”.
Israeli tanks and warplanes bombarded the Gaza Strip yesterday, as Hamas militants stuck to their demand for the lifting of an Israeli and Egyptian blockade amid US efforts to reach a cease-fire.
The 16-day conflict has claimed the lives of 729 Palestinians, most of them civilians, Palestinian health officials say. Israel has lost 32 soldiers, all since July 17, when it widened its air campaign into a full-scale ground operation aimed at halting rocket fire from Gaza and destroying a sophisticated network of cross-border tunnels.
Two Israeli civilians and a Thai worker in Israel have also been killed.
Appearing with visiting British Foreign Secretary Philip Hammond, Israeli Prime Minister Benjamin Netanyahu made no reference to the cease-fire efforts in underscoring his determination to neutralize the rocket and tunnel threats.
More than 2,000 rockets have been fired at Israel from Gaza since July 8, and the Israeli military says it has uncovered more than 30 tunnels leading from Gaza to Israel, some of which have been used by Hamas to carry out attacks.
“We started this operation to return peace and quiet to Israel,” Netanyahu said in Jerusalem. “And we shall return it.”
Six members of the same family and an 18-month-old infant boy were killed when an Israeli airstrike hit the Jebaliya refugee camp in the early morning hours, according to Gaza police and health officials. Twenty others were injured in the strike, they said, and rescuers were digging through the rubble of flattened homes, looking for survivors.
Heavy fighting was reported along the border of central Gaza, according to Gaza police spokesman Ayman Batniji. Israeli troops fired tank shells that reached parts of the Bureij and Maghazi refugee camps. There were no immediate reports of injuries.
Clashes also erupted between Palestinian fighters and Israeli troops in the northern town of Beit Lahiya, and the sound of explosions was audible across the town, Batniji said.