GAZA CITY, Gaza Strip (AP) — Thousands of Palestinian residents of the northern Gaza Strip fled their homes yesterday and sought safety in UN shelters, heeding warnings from the Israeli military about impending plans to bomb the area in the sixth day of an offensive against Hamas that has killed more than 160 people.

The fighting showed no signs of slowing, despite international calls for a ceasefire and growing concerns about the mounting civilian death toll in Gaza. US Secretary of State John Kerry spoke to Israeli Prime Minister Benjamin Netanyahu and voiced US “readiness” to help restore calm, while Egypt, a key mediator between Israel and Hamas, continued to work behind the scenes.

Amid the diplomacy, Israel said it was pushing forward with preparations for a possible ground invasion of Gaza. Thousands of troops have massed along the border in recent days.

“We don’t know when the operation will end,” Israeli Prime Minister Benjamin Netanyahu told his Cabinet yesterday. “It might take a long time.” He said the military was prepared “for all possibilities”.

Israel launched the offensive last Tuesday in what it said was a response to heavy rocket fire out of Hamas-controlled Gaza. The military says it has launched more than 1,300 airstrikes, while Palestinian militants have launched more than 800 rockets at Israel. The Palestinian Health Ministry in Gaza says 166 people have been killed, including dozens of civilians. There have been no Israeli fatalities, though several people have been wounded, including a teenage boy who was seriously wounded by rocket shrapnel yesterday.

Early Sunday, the Israeli air force dropped leaflets around the northern Gaza town of Beit Lahia ordering people to evacuate their homes. Israel says much of the rocket fire has come from the area, and overnight Sunday, the military carried out a brief ground operation on what it said was a rocket-launching site that could not be struck from the air. Four Israeli soldiers were lightly wounded before returning to Israeli.

The UN refugee agency for Palestinians, UNRWA, said some 17,000 Palestinians had headed to special shelters set up in 20 United Nations schools in Gaza.

“The fact that in a span of almost a few hours, 10,000 people sought refuge in these 15 schools is an indication to the difficult situation on the ground,” said Sami Mshasha, a UNRWA spokesman.

Some raced by in pickup trucks, waving white flags. “Once we received the message, we felt scared to stay in our homes. We want to leave,” said one resident, Mohammed Abu Halemah.