JERUSALEM/NEW YORK/TEL AVIV (Reuters) -Israel called on Friday for all civilians in the northern half of the Gaza Strip, more than 1 million people, to relocate south within 24 hours, as it amassed tanks for an expected ground assault in response to an attack by the militant group Hamas.

Hamas, which controls the strip, told residents to stay put, and vowed to fight to the last drop of blood. By Friday afternoon there was no sign of any mass exodus as Israel prepared its onslaught.

"Death is better than leaving," said Mohammad, 20, standing in the street outside a building reduced to rubble in an Israeli air strike two days ago near the centre of Gaza.

"I was born here, and I will die here, leaving is a stigma."

The United Nations said evacuating everyone was impossible with power supplies cut and food and water in the Palestinian enclave running short after a week of retaliatory air strikes and a full Israeli blockade. The U.S. called it a "tall order".

The northern half of the Gaza Strip includes the enclave's biggest settlement Gaza City. The U.N. said it had been told that Israel wanted the entire population to move across the wetlands that bisect the enclave.

"Civilians of Gaza City, evacuate south for your own safety and the safety of your families and distance yourself from Hamas terrorists who are using you as human shields," the Israeli military said, accusing Hamas of hiding in and under civilian buildings.

Mahmoud Abbas, President of the Palestinian Authority that is a rival of Hamas, told U.S. Secretary of State Antony Blinken in Jordan that the forced displacement of Palestinians in Gaza would constitute a repeat of 1948, when hundreds of thousands of Palestinians fled or were driven from what is now Israel. Most Gazans are the descendants of such refugees.

Abbas called for aid to be allowed into Gaza immediately. Israel has said it will not lift its blockade until scores of hostages captured by Hamas are set free. The Red Cross has said hospitals could soon run out of emergency fuel.

IRAN WARNING

International talks focused on providing aid and safe zones in Gaza amid fears the conflict could spread, with Iran warning of a response from its allies, which include Hamas and the powerful Hezbollah movement in Lebanon.

Pro-Palestinian protests were held around the world and in some places, Jewish communities feared they could be targeted after Israel's military response to the unprecedented weekend attacks that killed more than 1,300 people, mostly civilians.

Israel has already responded with the most intensive air strikes of its 75-year conflict with the Palestinians. Gaza authorities say more than 1,500 people have been killed.

"We are ready to join the fight and rid the Palestinians of the Israeli atrocities," said Muntadhar Kareem, 25, a teacher among thousands of Iraqis protesting in Baghdad.

The Israeli military pledged to operate "significantly" in coming days.

"We are fighting for our home. We are fighting for our future," Defence Minister Yoav Gallant said. "The path will be long, but ultimately I promise you we will win."

Israel says the horrific attack on its civilians means it must annihilate the militant group and others must get out of the way. Hamas tunnels, military compounds, senior operatives' residences and weapons storage warehouses were among 750 military targets struck overnight, it said.

The military wing of Hamas said the latest air strikes had killed 13 of the captives it brought back from Israel and that it had fired 150 rockets at Israel in response.

The United Nations said Israel's call for Gaza civilians to leave could not happen "without devastating humanitarian consequences", prompting a rebuke from Israel which said it should condemn Hamas and support Israel's right to self-defence.

A ground invasion of the narrow and densely populated Gaza Strip, home to 2.3 million people, poses serious risk, with Hamas threatening to kill its hostages.

Hours after the Israeli evacuation call, there were no signs people were leaving Gaza City, where dozens gathered at the al-Shifa Hospital, vowing to stay put.

Palestinians in southern and central areas of the enclave, where people were expected to flee to, said air strikes had hit there overnight, with central parts also hit on Friday morning. "No place is safe in the entire Gaza Strip," the Palestinian Red Crescent Society said.

The U.N. humanitarian office (OCHA) said more than 400,000 people had already been made homeless in Gaza and 23 aid workers had been killed. "Mass displacement continues," it said.

The U.N. Palestinian refugee agency (UNRWA) said it had moved its central operations centre and international staff to Gaza's south and urged Israel to spare its shelters.