Yasser Arafat may have been killed with a lethal dose of the highly radioactive substance Polonium, it was claimed on Tuesday.
Tests performed by a Swiss laboratory found significant traces of Polonium-210 on the late Palestinian leader's clothes, adding a new twist to a case that has obsessed the Arab world for years.
Polonium-210 is the same substance used to poison the Russian dissident Alexader Litvinenko in London.
The claims are likely to renew Palestinian suspicions that Mossad, the Israeli spy agency, assassinated Arafat, who died in a Paris hospital in 2004.
The Institute de Radiophysique in Lausanne found a level of 180?millibecquerels of Polonium-210, more than 20 times the dose needed to kill a human, in bodily fluid on Arafat's clothes. "I can confirm to you that we measured an unexplained, elevated amount of unsupported Polonium-210 in the belongings of Arafat that contained stains of biological fluids," Dr Francois Bochod, the director of the institute, told Al Jazeera, the pan-Arab television station.
Al Jazeera sent Arafat's clothes to the institute for testing after obtaining them from his widow as part of a nine-month investigation into his death.
Many theories have been advanced in the past for the cause of his death, and his case notes - which are alleged to show that he had suffered cirrhosis - have never been released.
A former speech writer for George W Bush claimed he had contracted Aids from a homosexual relationship with one of his guards, while aides of Arafat have alleged that he was poisoned by Mossad with Thallium, another radioactive element.
Some of Arafat's symptoms, including vomiting, cirrhosis and coma, are compatible with Polonium-210 poisoning, which results in a long and agonising death. But it is not thought that Arafat suffered hair loss, which is thought to happen in half of cases of significant exposure to the element.
The dose allegedly ingested by Arafat was much smaller than the amount that killed Litvinenko.
British police dealing with the Litvinenko case have alleged that only a sophisticated, state-backed intelligence agency could source Polonium-210 in a form that could be used as poison.