RAMALLAH, Palestinian Territories (AFP) - Palestinian officials demanded a global probe into the "killing" of Yasser Arafat on Thursday as Swiss experts said test results showed "moderate" backing for the theory he had been poisoned.

With the scientific analysis purportedly showing how the Palestinian leader had died, a senior figure in the Palestine Liberation Organisation called for an international inquiry to determine who was responsible.

But speaking to reporters in Lausanne, the Swiss team said the test results neither confirmed nor denied that polonium was the actual source of his death, although they provided "moderate" backing for the idea he was poisoned by the rare and highly radioactive element.

And they said the quantity of the deadly substance found on his remains pointed to the involvement of a third party.

"We can't say that polonium was the source of his death... nor can we rule it out," said Professor Francois Bochud of the Lausanne Institute of Applied Radiophysics.

Prof Bochud's lab, which is part of Switzerland's respected Vaudois University Hospital Centre, measured levels of polonium up to 20 times higher than it is used to detecting.

"By definition, that indicates third-party involvement," he said.

"Our results offer moderate backing for the theory of poisoning."

Arafat died in France on November 11, 2004 at the age of 75 after falling sick a month earlier, but doctors were unable to specify the cause of death.