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Yasser Arafat's murder inquiry was triggered by a Swiss institute finding high levels of polonium-210 on his clothing supplied by his widow, Suha.
However, the Institut de Radiophysique in Lausanne responded that symptoms described in Mr Arafat's medical reports were not consistent with the element.
Suha Arafat's lawyer, Marc Bonnant, said the tests in Switzerland "showed that Mr Arafat, in all likelihood, died through poisoning."
He added: "This hypothesis must be proved, and if that's the case, then it's premeditated murder."
Mr Arafat was confined by Israel to his compound after a Palestinian uprising and was already in poor health when he collapsed in October 2004.
At first his aides said he was suffering from flu but, looking weak and thin, he was flown to France where he slipped into a coma and died on Nov. 11.
Despite many Arabs suspecting Israel of being behind Yasser Arafat's decline, Israeli Foreign Ministry spokesman Yigal Palmor distanced his nation from the French inquiry into the Palestinian leader's death.
Yet Mr Palmor said he hoped it would reveal more on the circumstances of Mr Arafat's death.
The Arab League will call at the United Nations for an international investigation into the 2004 death of Yasser Arafat, the chief negotiator for the Palestinian Authority has said.
Saeb Erekat, though, welcomed news that a French court had opened a murder inquiry into the death of the longtime Palestinian leader in a Paris military hospital eight years ago.
The inquiry follows claims by Mr Arafat's widow, Suha, that he may have been poisoned with the radioactive element polonium-210. The same substance infamously killed former Russian spy Alexander Litvinenko in 2006.
French prosecutors will investigate claims Palestinian leader Yasser Arafat was poisoned to death in Paris in 2004, AFP has reported.
The murder inquiry came after Mr Arafat's family began legal action over the allegation that he died at a military hospital of radioactive poisoning.
It was reported last month that highly toxic polonium was found on the Nobel Peace Prize laureate's personal effects at the time of his death eight years ago.