The scientists of the Vaudois University Hospital Center in Lausanne, Switzerland, explained to international media on Thursday that they had found significant quantities of radioactive Polonium-210 and of lead in Yasser Arafat's remains.

But they also clarified, they had found no scientific evidence to prove without doubt that he died from that radioactive substance.

Arafat died in November 2004 at the age of 75, after he had fallen ill while living in his compound in the West Bank, where the Israeli authorities kept him under siege for the last two-and-a-half years of his life. Doctors at the time said they were unable to verify the cause of his death and no autopsy was carried out.

Samples for the investigation were taken from Arafat's remains in November last year, at the request of Arafat's wife Suha.

The Swiss scientists on Thursday said they saw parallels to the assassination of Russian former spy Alexander Litvinenko in London in 2006, who was found by a British inquiry that he died after polonium was dropped into his tea.

The results of the Swiss study were first published by the television channel Al-Jazeera on Wednesday, and were understood to suggest that poisoning could not be ruled out. This prompted calls by Palestinian officials for an international probe, with many Palestinians again accusing Israel of assassinating their leader.

"The results proved Arafat was poisoned by polonium and this substance is owned by states, not people, meaning that the crime was committed by a state," said the PLO's Wasel Abu Yusef in a first reaction.

Israeli officials were quick to reiterate their long standing denial of any involvement.

Polonium can be a byproduct of the chemical processing of uranium in a nuclear reactor. Israel has a nuclear research center and is believed to have a nuclear arsenal.

Yasser Arafat's widow Suha vowed to continue with the investigation into her husband's death, which she refers to as “a real crime, a political assassination."

The Palestinian authority has announced it would hold a press conference on the matter on Friday.

rg/hc (AFP, Reuters, AP)