The UN's human rights chief says he's horrified by the destruction of two of Gaza's main hospitals, amid reports of mass graves being found at the sites. Palestinian officials say they've exhumed the bodies of almost 300 people at Nasser and Al-Shifa hospitals. The Israel Defense Forces, described as baseless and unfounded, reports that they buried bodies and said existing graves had been opened while searching for the remains of hostages. Our special correspondence, Fergal Keen, reports, and a warning some viewers might find images in his report distressing.

Bom into brokenness. Khan Younes today from above. And down among the ruins, a mother and sister search for a missing son. Nabil Zaidan, aged 23, was killed in January. His mother, Reem, and sister Mai, have been searching for Nabil's body ever since.

For two weeks since Israeli When the resources left here, they've come to the Nasser Hospital.

Even if he's a dead body, I want my son. Just bring me my son. My heart has been broken for the past three months since I lost him.

This is a place where nobody comes in hope of finding the living. Only if they're lucky, the dead, and an end to searching whose trauma is difficult to comprehend.

I saw bodies that had signs of torture.

They were executed. Some had their hands and legs tied together and were executed. How long will this continue?

The graves are now at the center of conflicting claims between Hamas and local aid workers on one side and the Israel Defense Forces on the other. Hamas claims some of the dead were executed. The Israelis describe these allegations as baseless, saying they'd opened existing graves to check for dead Israeli hostages.

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

Colleagues at BBC Verify have confirmed the existence of graves at the hospitals before Israel began its operations in both complexes. Buried like this because staff couldn't reach cemeteries due to fighting in the area. Today, a senior UN official told me there had to be an independent investigation to establish the facts.

What we cannot allow in this current situation, where we have seen in Gaza numerous grave human rights violations, many of them potentially war crimes, and where we have raised alarm of potential atrocity crimes, that this becomes another blip. The intensity city of violations have been massive.

It is early afternoon at Al-Nassr Hospital, and Reem has been directed to this section of the graveyard. Nabil might be here. Nabil, I swear it's him. It's his jacket. My son, my son, I found him, she says. My life, my heart, my son. To rejoice that your dead child has been lifted from an anonymous grave. That is a measure of the agony engulfing Gaza. Fragil Keen, BBC News, Jerusalem.