MOSCOW — A Russian investigation into the death of Palestinian leader Yasser Arafat has found that his death was not caused by radiation.
The finding followed a French inquiry that found traces of the radioactive isotope polonium in Arafat’s body and a Swiss investigation that said the timing of his illness and death was consistent with that of polonium poisoning.
Vladimir Uiba, the head of the Federal Medical and Biological Agency, said Thursday that Arafat died of natural causes and the agency had no plan to conduct further tests.
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.
French specialists found traces of polonium but said it was ‘‘of natural environmental origin,” according to Arafat’s widow, Suha Arafat. 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.
‘‘It was a natural death; there was no impact of radiation,” Uiba said, according to Russian news agencies.
There was no explanation as to how the three investigations could have led to different conclusions.
Palestinians have long suspected Israel of poisoning Arafat, which Israel denies. Russia, meanwhile, has had strong ties with Palestinian authorities since Soviet times, when Moscow supported their struggle.
Dr. Abdullah Bashir, the head of the Palestinian medical committee investigating Arafat’s death, said they were studying the Russian and Swiss reports.
‘‘When we finish we are going to announce the results,” Bashir said by phone from Amman, Jordan. He did not say when that might be.
Arafat’s widow filed a legal complaint in France seeking an investigation into whether he was murdered after a 2012 report said traces of polonium were found on his clothes.
As part of that inquiry, French investigators had Arafat’s remains exhumed and ordered tests on them.
Polonium occurs naturally in very low concentrations in the earth’s crust and is produced artificially in nuclear reactors. There are also tiny, generally undetectable amounts of polonium in humans.
The Palestinian ambassador to Russia, Fayed Mustafa, was quoted by state RIA Novosti news agency Thursday as saying that the Palestinian authorities respect the Russians’ conclusions but consider it necessary to continue research into Arafat’s death.
Uiba said, however, that his agency has not 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 is made artificially in a nuclear reactor or a particle accelerator. Dozens of countries including Russia, Israel, and the United States have the nuclear capability to produce polonium.