The United Nations’ human rights office on Tuesday called for an independent investigation into two mass graves found after Israeli forces withdrew from hospitals in Gaza, including one discovered days ago over which Israeli and Palestinian authorities offered differing accounts.

Palestinian Civil Defense said over the weekend that it had found a mass grave containing 283 bodies on the grounds of Nasser Hospital in the southern city of Khan Younis, two weeks after a similar mass grave was found at Al-Shifa Hospital in Gaza City.

Mahmoud Basal, a spokesman for Palestinian Civil Defense — an emergency services organization run by the Palestinian Authority, a rival to Hamas — said some of the bodies found in Khan Younis were handcuffed, shot in the head or wearing detainee uniforms. He accused Israeli forces of killing and burying them. Israel’s military declined to address those claims on Tuesday, and they could not be independently verified.

On Tuesday, hours after the top U.N. human rights official called for an inquiry into the mass graves, the Israeli military said that its forces had exhumed bodies that were buried by Palestinians “in the area” of Nasser Hospital and examined them as part of an effort to locate hostages. It did not comment on the report of the mass grave at Al-Shifa.

The Israeli military declined to say how many bodies troops had exhumed and reburied, how they died or whether the remains of any hostages had been found at the site. It also did not say how the bodies had been examined to determine if they were those of Israeli hostages.

“The examination was carried out respectfully while maintaining the dignity of the deceased,” the statement said. “Bodies examined, which did not belong to Israeli hostages, were returned to their place.”

It was not clear where the people discovered in the mass grave were originally buried. But wartime chaos in Gaza has made it common for Palestinians to bury the dead in mass graves or in courtyards and back gardens in a hurried way that might be unthinkable in times of peace.

In January, an official at Nasser told journalists that hospital workers had buried about 150 people in the hospital yard because nearby fighting had made it too dangerous to travel to a cemetery.

The discovery of the mass grave at Nasser Hospital came two weeks after a mass grave was reported to have been discovered at Al-Shifa Hospital in Gaza City after an Israeli military operation there. The U.N. human rights office said on Tuesday that the Gaza government had reported that another 30 bodies were found in two graves there, 12 of which had been identified. The office said it could not confirm the accounts.