Heavy fighting between Israeli troops and Palestinian militants on the outskirts of the southern Gaza city of Rafah has left crucial nearby aid crossings inaccessible and forced more than 110,000 people to flee north, U.N. officials said Friday.

With nothing entering through the crossings, food and other supplies were running critically low, aid agencies said.

The World Food Program will run out of food for distribution in southern Gaza by Saturday, said Georgios Petropoulos, an official with the U.N. Office for Coordination of Humanitarian Affairs in Rafah. Aid groups have said fuel will also be depleted soon, forcing hospitals to shut down critical operations and bringing to a halt trucks delivering aid across south and central Gaza.

The United Nations and other agencies have warned for weeks that an Israel assault on Rafah, on the border with Egypt near the main aid entry points, would cripple humanitarian operations and cause a disastrous surge in civilian casualties. More than 1.4 million Palestinians — half of Gaza's population— have been sheltering in Rafah, most after fleeing Israel's offensives elsewhere.

Heavy fighting was also underway Friday in northern Gaza, where Hamas appeared to have once again regrouped in an area where Israel has already launched punishing assaults.

Israel's move into Rafah has been short of the full-scale invasion that it has planned. The United States is deeply opposed to a major offensive and is stepping up pressure by threatening to withhold arms to Israel.

But the heavy fighting has shook the city and spread fear that a bigger assault is coming. Artillery shelling and gunfire rattled throughout the night into Friday, an Associated Press reporter in the city said.

The U.N. agency for Palestinian refugees, known as UNRWA, said more than 110,000 people have fled Rafah. Families who have already moved multiple times during the war packed up to go again. One woman held a cat in her arms as she sat in the back of a truck piled with her family's belongings about to head out.

The full invasion hasn't started "and things have already gotten below zero," said Raed al-Fayomi, a displaced person in Rafah. "There's no food or water."

Those fleeing erected new tents camps in the city of Khan Younis — which was half destroyed in an earlier Israeli offensive — and the town of Deir al-Balah, straining infrastructure.

The international charity Project Hope said its medical clinic in Deir al-Balah had seen a surge in people from Rafah seeking care for blast injuries, infections and pregnancies. "People are evacuating to nothing. There are no homes or proper shelters for people to go to," said the group's Gaza team leader based in Rafah, Moses Kondowe.

Petropoulos said humanitarian workers had no supplies to help them set up in new locations. "We simply have no tents, we have no blankets, no bedding, none of the items that you would expect a population on the move to be able to get from the humanitarian system," he said.

Israeli troops captured the Gaza side of the Rafah crossing with Egypt on Tuesday, forcing it to shut down. Rafah was the main point of entry for fuel.

Israel says the nearby Kerem Shalom crossing — Gaza's main cargo terminal — is open on its side, and that aid convoys have been entering. It said trucks carrying 200,000 liters of fuel were allowed to enter the crossing Friday.

But the U.N. said it is too dangerous for workers to reach the crossing on the Gaza side to retrieve the aid because of Israel's incursion and the ensuing fighting with Hamas.

Israeli troops are also battling Palestinian militants in eastern Rafah, not far from the crossings. The military said it had located several tunnels and eliminated militants in close combat and with airstrikes.

Hamas' military wing said it struck a house where Israeli troops had taken up position, an armored personnel carrier and soldiers operating on foot. There was no comment from the Israeli military,

It is not possible to independently confirm battlefield accounts from either side.

Hamas also said it launched mortar rounds at troops near the Kerem Shalom crossing. The military said it intercepted two launches. The crossing was initially closed after a Hamas rocket attack on nearby forces last weekend killed four Israeli soldiers.

Hamas rockets also reached the southern Israeli city of Beersheeva on Wednesday, lightly injuring a woman with shrapnel, Israel's military and rescue services said Friday. Five rockets were fired toward the city, with one intercepted and most falling in open areas, the military said. Through much of the war, Gaza militants fired thousands of rockets from Gaza on Israeli cities and towns, most of them intercepted, but such attacks have grown rarer in past months.

Israel says Rafah is the last Hamas stronghold in Gaza and key to its goal of dismantling the group's military and governing capabilities and returning scores of hostages Hamas captured in its deadly Oct. 7 attack that triggered the war.

But Hamas has repeatedly regrouped, even in the hardest-hit parts of Gaza.

Heavy battles erupted this week in the Zeitoun area on the outskirts of Gaza City, in the northern part of the territory. Northern Gaza was the first target of the ground offensive, and Israel said late last year that it had mostly dismantled Hamas there.

The north remains largely isolated by Israeli troops, and the U.N. says the estimated 300,000 people there are experiencing "full-blown famine."

Israeli Prime Minister Benjamin Netanyahu has vowed to proceed with the Rafah offensive with or without U.S. arms, saying "we will fight with our fingernails" if needed, in a defiant statement late Thursday. The U.S. has stepped up weapons deliveries to Israel throughout the war, and the Israeli military says it has what it needs for Rafah operations.

The war began with Hamas' surprise attack into southern Israel last year, in which the militants killed some 1,200 people, mostly civilians, and took another 250 hostage. They are still holding some 100 captives and the remains of more than 30, after most of the rest were released during a cease-fire last year.

Israel's bombardment and ground offensives in Gaza have killed more than 34,800 Palestinians, mostly women and children, according to the Gaza Health Ministry, which does not distinguish between civilians and combatants in its figures. Much of Gaza has been destroyed and some 80% of Gaza's population has been driven from their homes.

Israel's incursion into Rafah complicated what had been months of efforts by the U.S., Qatar and Egypt to broker a cease-fire and the release of hostages. Hamas this week said it had accepted an Egyptian-Qatari cease-fire proposal, but Israel says the plan does not meet its "core" demands. Follow-up talks appeared to end inconclusively on Thursday.

Hamas has demanded guarantees for an end to the war and a full Israeli withdrawal from Gaza as part of any deal — steps that Israel has ruled out.

___

Krauss reported from Jerusalem. Associated Press writer Stephen Graham in Berlin contributed to this report.