Gaza's civil defence said on Sunday health workers had uncovered at least 50 bodies of people killed and buried by Israeli forces at a hospital in the southern city of Khan Younis.

Israel's military said it was checking the reports.

In a statement, the civil defence agency said the remains were discovered in the courtyard of the Nasser Medical Complex.

"Inside the Nasser Medical complex there are mass graves dug by the Israeli occupation ... we were shocked by the presence of bodies of 50 martyrs in one of the pits yesterday," Mahmud Bassal, spokesman for the civil defence agency, said.

"We are continuing the search operation today and are waiting for all graves to be exhumed in order to give a final number of martyrs."

He alleged some of those killed had been tortured.

"There were no clothes on some bodies, which certainly indicates (the victims) faced torture and abuse," Bassal said.

Intense fighting raged in mid-February in the area of the hospital, and Israeli tanks and armoured vehicles surrounded it on March 26.

In a separate statement on Sunday, Hamas condemned what it said was a "mass grave of those executed in cold blood and buried with military bulldozers in the hospital's courtyard."

It said more than 50 bodies had been recovered there.

Several of the bodies wrapped in white shrouds were later collected by relatives.

Hospitals in Gaza have not been spared in the Israeli assault, with the military accusing Hamas of using the facilities as command centres and to hold hostages abducted in the October 7 attack.

The World Health Organisation said on April 6 that the Palestinian territory's largest hospital, Al-Shifa in Gaza City, had been reduced to ashes by an Israeli siege last month, leaving an "empty shell" containing many bodies.

WHO staff who gained access to the devastated facility described horrifying scenes of bodies only partly buried, their limbs sticking out, and the stench of decomposition.

Israel is engaged in a sweeping military assault against Hamas militants in Gaza after they launched a attack on southern Israeli communities on October 7.

The unprecedented assault resulted in the deaths of 1,170 people, Israelis and foreigners, according to a tally based on official Israeli figures.

Some 250 people were abducted to Gaza during the attack, of whom 129 remain captive, including 34 the Israeli military says are dead.

Israel's retaliatory offensive has so far killed 34,097 people in Gaza, mostly women and children, according to the Hamas-run territory's health ministry. (AFP)