The BBC's Yolande Knell: "The scientists themselves are extremely cautious"
Q&A: Investigation into Yasser Arafat's death
Yasser Arafat's remains exhumed
Obituary: Yasser Arafat
The late Palestinian leader Yasser Arafat may have been poisoned with radioactive polonium, says a Swiss forensic report obtained by al-Jazeera.
Arafat's official medical records say he died in 2004 from a stroke resulting from a blood disorder.
But his body was exhumed last year amid continuing claims he was murdered.
The Swiss report said tests on the body showed "unexpected high activity" of polonium, which "moderately" supported the poisoning theory.
Many Palestinians and others have long believed that Israel poisoned Arafat. Others allege that he had Aids or cancer. Israel has consistently denied any involvement.
A spokesman for the Israeli foreign ministry said the Swiss investigation was "more soap opera than science".
'Hole in theory'
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Swiss scientists' findings
Experts at the Vaudois University Hospital Centre (CHUV) in Lausanne, Switzerland, conducted tests on samples taken from Yasser Arafat's exhumed body in November 2012
Samples also analysed by Palestinian, French and Russian teams, whose findings have yet to be published by the Palestinian Authority
Swiss report says "unexpectedly high levels of polonium-210 and lead-210 activity" found in specimens taken from Arafat's ribs, pelvis and soil that absorbed his bodily fluids
It notes a lack of adequate biological specimens, particularly soft tissues, and the eight years between death and the investigation, rendering detection subject to uncertainties
But it concludes results "moderately support the proposition that the death was the consequence of poisoning with polonium-210"
Q&A: Exhumation of Yasser Arafat
The scientists - from the Vaudois University Hospital Centre (CHUV) in Lausanne, Switzerland - carried out a detailed examination of Arafat's medical records, samples taken from his remains and items he had taken into the hospital in Paris where he died in 2004.
The biological materials included pieces of Mr Arafat's bones and soil samples from around his corpse.
The scientists concluded that their results "moderately support the proposition that the death was the consequence of poisoning with polonium-210".
The scientists stressed that they had been unable to reach a more definitive conclusion because of the time that had lapsed since Arafat's death, the limited samples available and the confused "chain of custody" of some of the specimens.
Polonium-210 is a highly radioactive substance. It is found naturally in low doses in food and in the body, but can be fatal if ingested in high doses.
The scientists have made "a pretty strong statement", according to Prof Paddy Regan, an expert in radiation detection and measurement at the University of Surrey in the UK, who was not involved in the investigation.
"They are saying the hypothesis that Arafat was poisoned with polonium-210 is valid and has not been disproven by the data. However they cannot say definitively that he was murdered."
Prof Regan says a series of assumptions would have been made in order to ascertain how much Po-210 may or may not have been in Mr Arafat's body at the time of his death.
Yasser Arafat's widow, Suha: "I felt shock and anger and huge sadness" - Video courtesy al-Jazeera
Po-210 has a short half-life of about 138 days.
Prof Regan said measuring the tiny fraction left and extrapolating it back to the time of Arafat's death was like a blind man holding the tail of an elephant and using the information to work out the size of the animal.
The second problem, he said, was that Po-210 occurs naturally in the environment. However, an indicator that the polonium may be synthetic is if there was far less Pb-210 (lead-210) in the samples.
The professor highlighted results from two samples - the shroud under the corpse of Mr Arafat and urine samples taken from his underwear - both showed high levels of Po-210 compared to Pb-210, possibly suggesting the presence of "additional" synthetic polonium.
He noted however that most of the samples of polonium measured in the report were accompanied by activities from Pb-210.
Parallel investigations are being carried out by French and Russian experts - one Russian official said last month that no traces of polonium had been found.
Yigal Palmor of Israel's foreign ministry told the BBC: "This is more soap opera than science."
Arafat's tomb in Ramallah was opened in private in November last year
He said the investigations had been commissioned by "interested parties" - Mr Arafat's widow and the Palestinian Authority - and had "never bothered" to look for some key data.
"The other huge hole in the theory is the absence of all access to the French hospital where Arafat died and to Arafat's medical files," said Mr Palmor.
"How can the cause of death be determined without the opinion of the doctors or the results of the medical tests they ran on the patient?
"Israel doesn't feel concerned in the least."
Speaking in Paris, Arafat's widow, Suha, said the Swiss results revealed "a real crime, a political assassination".
Highly radioactive and toxic element
Present in foods in low doses
Small amounts created naturally in the body
Can be manufactured by bombarding certain isotopes with neutrons
Has industrial uses such as in anti-static devices
Very dangerous if significant dose ingested
External exposure not a risk, only if ingested
Present in tobacco
What is polonium-210?
"This has confirmed all our doubts. It is scientifically proved that he didn't die a natural death and we have scientific proof that this man was killed."
Reuters said she did not name any suspects and acknowledged that her husband had had many enemies in his lifetime.
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.
France began a murder inquiry in August 2012 after the Lausanne scientists, working with an al-Jazeera documentary crew, found traces of polonium-210 on Arafat's personal effects.
His widow had objected to a post-mortem at the time of his death, but asked the Palestinian Authority to permit the exhumation "to reveal the truth".
His remains were removed from his tomb in the West Bank city of Ramallah in November 2012 and reinterred the same day.
Last month, the head of the Russian Federal Medico-Biological Agency, Vladimir Uiba, was quoted by the Interfax news agency as saying that Arafat "could not have been poisoned with polonium", saying that test carried out by Russian experts "found no traces of this substance".
However, the agency later denied that Mr Uiba had made any official statement on the findings.
The head of the Palestinian investigation team, Tawfiq Tirawi, confirmed on Tuesday that the Russian and Swiss reports had been delivered. The Palestinian team is reported to have handed over its findings on Saturday.