PARIS -- Extensive reports by French scientists into Palestinian leader Yasser Arafat's death have ruled out poisoning by radioactive polonium, his widow said Tuesday. The results contradict earlier findings by a Swiss lab, and mean it's still unclear how Arafat died nine years ago.

Scientists from several countries have tried to determine whether polonium played a role in his death in a French military hospital in 2004. Palestinians have long suspected Israel of poisoning him, which Israel denies.

After a 2012 report that traces of radioactive polonium were found on Arafat's clothing, Arafat's widow filed a legal complaint in France seeking an investigation into whether he was murdered.

As part of that investigation, French investigators sought Arafat's remains exhumed and ordered genetic, toxicology, medical, anatomical and radiation tests on them. Suha Arafat and her lawyers were notified Tuesday of the results.

She told reporters in Paris that they exclude the possibility of poisoning by polonium, a rare and extremely lethal substance. She said the French investigators don't rule out the possibility that he died of natural causes.

This is the latest in a string of recent expert reports on Arafat's death: A Swiss lab said that Arafat was probably poisoned by polonium. A Russian report given to Palestinian officials was inconclusive about polonium's role. But both the Swiss and Russian reports said his death was caused as a result of a toxic substances, not natural causes.

Suha Arafat said she's "upset by these contradictions by the best European experts on the matter." It's unclear how the experts' report could weigh on the French murder investigation, which is still ongoing.

The French experts found traces of polonium in their examination but came to "diametrically opposed conclusions" from the Swiss about where it came from, Suha Arafat's lawyer Pierre-Olivier Sur said.

Arafat died Nov. 11, 2004 at a French military hospital, a month after falling ill at his West Bank headquarters. At the time, French doctors said he died of a stroke and had a blood-clotting problem, but records were inconclusive about what caused that condition.