The body of Palestinian leader Yasser Arafat is to be exhumed on Tuesday, Palestinian officials say.
His body is to undergo tests to find out whether his death in Paris in 2004 was caused by poisoning.
Arafat's medical records say he had a stroke resulting from a blood disorder.
But France began a murder inquiry in August after Swiss experts hired by a documentary crew found radioactive polonium-210 on Arafat's personal effects. Continue reading the main story Analysis image of Richard Galpin Richard Galpin BBC News, Ramallah
The chief investigator Taufik al Tirawi said they had recently asked the Russians to take part in this investigation because they had "an historical relationship" with Moscow.
It seems the Palestinians do not fully trust France and Switzerland when it comes to proving or disproving that their former leader was murdered.
It is not known how long it will take the three countries to complete their tests. But it will be a key moment - and it is possible they will reach different conclusions.
While most Palestinians are certain their leader was murdered, there are serious questions about the validity of testing for polonium poisoning eight years after Mr Arafat's death. The half-life of polonium is less than five months.
His tomb, in Ramallah in the West Bank, was sealed off earlier this month.
Once the body is removed from the tomb inside the stone-clad tomb mausoleum, scientists from France, Switzerland and Russia will each take samples, former Palestinian intelligence chief Tawfik Tirawi told reporters.
The experts will then take these samples to their respective countries to be tested for Polonium 210 and possibly other lethal substances.
Arafat's body will be reburied the same day with military honours.
Arafat, who led the Palestine Liberation Organisation for 35 years and became the first president of the Palestinian Authority in 1996, fell violently ill in October 2004 at his compound.
Two weeks later he was flown to a French military hospital in Paris, where he died on 11 November 2004, aged 75.
His widow, Suha, objected to a post-mortem examination at the time, but later appealed to the Palestinian Authority to permit the exhumation "to reveal the truth".
Many Palestinians continue to believe that Israel poisoned him. Israel has denied any involvement. Others allege that he had Aids.
In 2005, the New York Times obtained a copy of Arafat's medical records, which it said showed he died of a massive haemorrhagic stroke that resulted from a bleeding disorder caused by an unknown infection.
Independent experts who reviewed the records told the paper that it was highly unlikely that he had died of Aids or had been poisoned.
A murder inquiry was launched by French prosecutors in August after an investigation by al-Jazeera TV, working with scientists at the Institute of Radiation Physics (IRA) at the University of Lausanne in Switzerland, found "significant" traces of polonium-210 present in samples taken from Arafat's personal effects, including his trademark keffiyeh headdress.
In some cases, the elevated levels were 10 times higher than those on control subjects, and most of the polonium could not have come from natural sources, the scientists said.
But the institute also said Arafat's symptoms - as described in medical reports - were not consistent with polonium poisoning.