"He could not have died of polonium poisoning - the Russian experts found no traces of this substance," Vladimir Uiba, the head of Russia's Federal Medical-Biological Agency, told the Interfax news agency on Tuesday.

The findings differ from ones formally published last week in Britain's The Lancet medical journal.

Swiss scientists said in the journal that polonium poisoning could not be ruled out. However, their conclusion was based not on samples from Arafat's body, but rather on samples from items handed to them by his widow, Suha Arafat.

The scientists from the Institute of Radiology in Lausanne, Switzerland said that they took 38 samples from Arafat's belongings, including from body fluids on his underwear and toothbrush.

Several of the blood and urine samples examined contained high levels of the radioactive element, raising the possibility that he could have been poisoned.

These tests were done before Arafat's body was exhumed in November 2012. Samples from his corpse were given to French, Swiss and Russian forensic experts to determine whether he was poisoned.

Suha Arafat first made the accusation that Israel used polonium to poison her late husband in an interview with al-Jazeera in July 2012.

Arafat died at the age of 75 in a French hospital on November 11, 2004. Medical records show he died of a brain hemorrhage, caused by a bowel infection.

Polonium-210 is a rare radioactive element, many times more toxic than other poisons such as cyanide.

Officials in Ramallah were not immediately available for comment because of the Muslim Eid al-Adha holiday.

Israel's Foreign Ministry said it preferred to wait for a Palestinian Authority reaction before commenting.

When the Palestinian leader fell ill, at the height of the second Palestinian uprising, he was under siege at his West Bank headquarters after having been declared an "obstacle to peace" by Israel.

NJF/NJF