French scientists investigating Palestinian leader Yasser Arafat's death have ruled out poisoning by radioactive polonium, his widow said, according to the Associated Press.

The results contradict earlier findings by a Swiss lab, and mean it is still unclear what killed Arafat 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 it denies.

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

As part of that investigation, French investigators had Arafat's remains exhumed and ordered genetic, toxicology, medical, anatomical and radiation tests on them. Suha Arafat and her lawyers were notified of the results Tuesday, December 3.

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 do not 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 he 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.

Mrs Arafat said she is "upset by these contradictions by the best European experts on the matter".

It is unclear how the experts' report could weigh on the French murder investigation, which is still going on.

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

Arafat died on November 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.