A Russian probe into the death of Palestinian leader Yasser Arafat has found no trace of radioactive poisoning, the chief of the government agency that conducted the study said Thursday.

Vladimir Uiba, the head of the Federal Medical and Biological Agency, said the agency had no plans to conduct further tests.

“It was a natural death; there was no impact of radiation,” Uiba said, according to Russian news agencies.

Teams of scientists from France, Switzerland and Russia were asked to determine whether polonium, a rare and extremely lethal substance, played a role in Arafat’s death in a French military hospital in 2004. Palestinians have long suspected Israel of poisoning him, which Israel denies. Russia, meanwhile, has had close ties with Palestinian authorities since Soviet times when Moscow supported their struggle.

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

As part of that probe, French investigators had Arafat’s remains exhumed and ordered a series of tests on them.

Suha Arafat, who was notified of the findings earlier this month along with her lawyers, said that the French experts found traces of polonium but came to different conclusions than the Swiss about where they came from, finding that it was “of natural environmental origin.”

Polonium occurs naturally in very low concentrations in the Earth’s crust and also is produced artificially in nuclear reactors.

Swiss scientists, meanwhile, said they found elevated traces of polonium-210 and lead, and that the timeframe of Arafat’s illness and death was consistent with poisoning from ingesting polonium.

Palestinian Ambassador to Russia, Fayed Mustafa, was quoted by state RIA Novosti news agency as saying Thursday that the Palestinian authorities respect the Russian experts’ conclusions but consider it necessary to continue research into Arafat’s death.

Uiba said, however, that his agency hasn’t received any Palestinian request for additional studies.

Arafat died Nov. 11, 2004, 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.

Polonium can be a byproduct of the chemical processing of uranium, but usually it’s made artificially in a nuclear reactor or a particle accelerator. Dozens of countries including Russia, Israel and the U.S. have the nuclear capability to produce polonium.

One of the most famous and recent cases of polonium-210 poisoning was that of ex-KGB officer Alexander Litvinenko who died in 2006 after drinking tea laced with the radioactive isotope.

Britain has accused two Russians of the 2006 killing, but Moscow has refused to extradite them.

(AP)