The United Nations called Monday for an independent inquiry into the death of a Palestinian in Israeli custody, warning that mounting tensions risk an eruption of violence in the occupied territories.

The Palestinians also demanded an independent investigation in a letter to the UN Security Council, which said that Arafat Jaradat, who died at the weekend, could have been tortured.

UN Middle East peace envoy Robert Serry made the call for an investigation in a statement after talks with Palestinian prime minister Salam Fayyad on the Jaradat's death.

Serry noted that Israeli and Palestinian experts had examined the body. "The United Nations expects the autopsy to be followed by an independent and transparent investigation into the circumstances of Mr Jaradat's death, the results of which should be made public as soon as possible," the envoy added.

Jaradat was detained on February 18 and died five days later.

Israeli prison authorities said Jaradat appeared to have died of a heart attack. But the Palestinian minister of prisoner affairs, Issa Qaraqaa, citing the preliminary findings of the joint autopsy, reported bruises on Jaradat's body, muscle damage and broken ribs.

A letter sent by Palestinian UN ambassador Riyad Mansour to the Security Council said the autopsy revealed that Jaradat "was subjected to severe beatings, abuse and medical negligence during his captivity, possibly amounting to torture."

The letter said Jaradat had six broken bones in his neck, spine, arms and legs, along with other injuries. Israel has said the prisoner could have suffered broken bones in attempts to resuscitate him after the heart attack.

"This horrific incident is further proof of the inhumane treatment systematically meted out by Israel against Palestinians in its jails," added the letter, which called for an "impartial investigation" and Security Council action to make Israel abide by humanitarian law.

Thousands attended the Jaradat's West Bank funeral on Monday and some militants have threatened revenge for his death.

Serry's statement said "mounting tensions present a real risk of destabilization".

UN leader Ban Ki-moon expressed concern last week about the deteriorating state of Palestinian hunger strikers in Israeli jails and said that the rights of all Palestinian detainees must be fully respected.