"We are still studying and investigating the details of the event and the reasons for the explosion," Israeli military spokesman Rear Admiral Daniel Hagari told reporters.

The assault came as Israeli forces pushed deep into western Khan Younis in Gaza, with an air, sea and land bombardment that included storming a hospital and arresting medical staff, Gaza health ministry spokesman Ashraf al Qidra told Reuters news agency.

At least 50 people were killed on Sunday night in Khan Younis, Mr Qidra said, adding the sieges at medical facilities meant rescuers could not reach the dead and wounded.

White House National Security Council spokesman John Kirby said on Monday that Israel had a right to defend itself, but added: "We expect them to do so in accordance with international law and to protect innocent people in hospitals, medical staff and patients as well, as much as possible."

The Israeli military has recently intensified strikes on Khan Younis in southern Gaza - which it believes is where top Hamas commanders are holed up.

Hamas militants crossed into Israel from the Gaza Strip in an unprecedented surprise assault, holding Israeli towns and military posts under siege, targeting a dance music festival, and killing and abducting civilians.

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