Israeli forces have been accused of executing handcuffed Palestinian medics before burying them in a mass grave underneath their crushed ambulances in southern Gaza's Rafah.

Fifteen humanitarian workers went missing last week after responding to a distress call from civilians being attacked by Israeli forces.

The workers include eight paramedics from the Palestine Red Crescent Society (PRCS), six members of the Palestinian Civil Defence search-and-rescue teams, and one UN staff member.

They were found over the weekend in a mass grave with at least around 20 multiple gunshots in each one of them, according to Mahmoud Basal, spokesperson for the Palestinian Civil Defence in Gaza.

At least one of them had their legs bound, another was decapitated and a third topless, he added.