There are different accounts of these mass graves, including serious allegations that some of those buried were killed illegally," Guterres said on Tuesday local time according to IRNA.
It is essential that independent international investigators with forensic expertise be allowed immediate access to the locations of these mass graves to determine the exact conditions in which hundreds of Palestinians died and were buried, he said, adding that "the families of the dead and the missing have the right to know what happened.
"The world has the right to seek accountability for any violations of international law that may have occurred," the Un chief added.
Palestinian civil defense teams recently discovered a mass grave in the complex of Nasser Hospital in Khan Yunis was taken over and bombed by Israeli forces for days. More than 300 bodies were discovered in this place of people killed and buried by Israeli forces.
Another mass grave was found in the vicinity of Shifa medical facility now containing the ruins after Israeli bombing and shelling of the complex.
The Euro-Mediterranean Human Rights Watch also announced in a report that more than 140 mass graves created by the Israeli military have been identified in the Gaza Strip.