CAIRO (Reuters) - Israel stepped up airstrikes on Rafah overnight, killing at least six Palestinians, medics said on Thursday, after saying it would evacuate civilians from the Gaza border city and storm it despite allies' warnings this could cause mass casualties.

In the seventh month of a devastating air and ground war against the Gaza Strip's ruling Islamist group Hamas, Israeli forces also resumed bombarding northern and central areas of the enclave, as well as east of Khan Younis in the south.

Israeli warplanes had hammered the north for a second day on Wednesday, shattering weeks of comparative calm there, and Israel said it was moving forward with plans for an all-out assault on Hamas holdouts in Rafah, on the southern border with Egypt.

Escalating Israeli threats to invade Rafah, the last refuge for around a million civilians who fled Israel's juggernaut further north earlier in the war, have nudged some families to leave for the nearby al-Mawasi coastal area or try to make their way to points further north, residents and witnesses said.

But the number of displaced people departing Rafah remained small with many confused over where they should go, saying their experience over the past 200 days of war had taught them that no place was genuinely safe.

Mohammad Nasser, 34, a father-of-three, said he had quit Rafah two weeks ago and now lived in a shelter in Deir Al-Balah in central Gaza to avoid being caught by surprise by an Israeli invasion and unable to escape.

"We escape from one trap into another, searching for places Israel calls safe before they bomb us there. It is like the rat and trap game," he told Reuters via a chat app.

"We are trying to adapt to the new reality, hoping it will become better, but I doubt it will."

Gaza medics and Hamas media reported five Israeli airstrikes on Rafah early on Thursday that hit at least three houses, killing at least six people including a local journalist.

Israeli tank fire on the main road near the town of Al-Zawyda in central Gaza killed four people, local medics said.

Meanwhile, a Palestinian civil defence team called on the United Nations to investigate what it said were war crimes at a Gaza hospital, saying nearly 400 bodies were recovered from mass graves after Israeli soldiers departed the complex in Khan Younis.

The Israeli military said claims by Palestinian authorities that its forces had buried the bodies were "baseless and unfounded".

BOMBING RESUMES

In the north, Israeli forces continued to pound Beit Lahiya, Beit Hanoun, Jabalia and Zeitoun, with some residents saying Hamas and Islamic Jihad militants were fighting Israeli ground forces with anti-tank rockets, mortar bombs and sniper fire.

The Palestine Telecommunications Company said Internet services had again been cut off in central and southern Gaza on Thursday, blaming Israeli military operations.

Such outages have compounded the obstacles confronting efforts to get emergency aid to stricken civilians and provide medical care at the few centres not yet shattered by fighting.

After an abrupt Israeli military pullback at the start of April, Palestinians at both ends of narrow, coastal Gaza were again fleeing for their lives this week from bombing they described as some of the war's worst.

On Wednesday, a spokesperson for Prime Minister Benjamin Netanyahu's government said Israel was "moving ahead" with its plans for a ground operation in Rafah but gave no timeline.

Western countries, including Israel's closest ally the United States, have pleaded with it to hold back from attacking the city, saying this could wreak a humanitarian disaster given the presence of many displaced people with only rudimentary shelter and little food or access to medical care.

A senior Israeli defence official said on Wednesday Israel was poised to evacuate civilians ahead of its attack and had bought 40,000 tents that could house 10-12 people each. All that remained was for Netanyahu to give the order.

The war, now in its seventh month, has killed at least 34,305 Palestinians, Gaza health authorities said in an update on Thursday. The offensive has laid to waste much of the densely populated and widely urbanised enclave, displacing most of its 2.3 million people and raising the spectre of famine.

Israel has vowed to eradicate Hamas since the Palestinian militant group's cross-border rampage on Oct. 7 in which 1,200 people were killed and 253 taken hostage, according to Israeli tallies.

(Writing by Mark Heinrich; editing by Alex Richardson)