Arafat's widow demanded that a Palestinian committee that has been investigating her husband's death now try to find "the real person who did it."

The committee also received a copy of the report, but declined comment.

The head of the committee, Tawfik Tirawi, said details would be presented at a news conference in two days, and that the Palestinian Authority, led by Arafat successor Mahmoud Abbas, would announce what it plans to do next.

An official in Abbas' Fatah movement raised the possibility of taking the case to the International Criminal Court. "We will pursue this crime, the crime of the century," said the official, Abbas Zaki.

Raanan Gissin, who was an Israeli government spokesman when Arafat died, reiterated Wednesday that Israel had no role in his death.

"It was a government decision not to touch Arafat at all," he said, adding that "if anyone poisoned him, it could have been someone from his close circle."

Arafat died Nov. 11, 2004, a month after falling violently ill at his Ramallah compound. French doctors said he died of a massive stroke and had suffered from a blood condition known as disseminated intravascular coagulation, or DIC. But the records were inconclusive about what led to the DIC, which has numerous possible causes, including infections and liver disease.

Polonium is a rare and highly lethal substance. A miniscule amount can kill. Its most famous victim was KGB agent-turned-Kremlin critic Alexander Litvinenko, who died in London in 2006 after the substance was slipped into his tea.

The examination of the Arafat's remains found "unexpectedly high levels" of polonium-210, the Swiss team wrote.

Derek Hill, a professor in radiological science at University College London who was not involved in the investigation, said the levels of polonium-210 cited in the report seem "way above normal."

"I would say it's clearly not overwhelming proof, and there is a risk of contamination (of the samples), but it is a pretty strong signal," he said. "It seems likely what they're doing is putting a very cautious interpretation of strong data."

He said polonium is "kind of a perfect poison" because it is so hard to detect unless experts look for it using specialized equipment generally found only in government laboratories.

Bruce Goldberger, director of health forensic medicine at the University of Florida, said the report was appropriately cautious in saying it had found moderate support for the idea that polonium poisoning killed Arafat. It does not prove that idea, he said.

Yet, "what they did was extraordinary" in view of the limitations they faced, he said. Those include the lack of fresh body tissue to analyze, the years of polonium decay that would leave only tiny amounts to look for and the lack of medical and scientific knowledge about polonium poisoning.

Goldberger noted that Arafat did not show some classic signs of radiation poisoning, further muddying the strength of the conclusion.

Lawrence Kobilinsky, a professor of forensic science at the John Jay College of Criminal Justice in New York, also said the report does not prove Arafat died from polonium. He noted that other scientific teams are expected to issue reports on the case.

"It looks like he's been poisoned, but I would wait for the other groups to confirm it," he said. "It's not done until we get a confirmation. This is how science works."

Nathan Lents, deputy chair of the department of sciences at John Jay, said the report's results are consistent with a possible polonium poisoning, but "there's certainly not a smoking gun here."