The Palestinian committee investigating the death of Yasser Arafat in 2004 has said Israel is the "only suspect".
A Swiss report published this week said specimens from Arafat's exhumed body contained unexpectedly high levels of the radioactive element, polonium-210.
The Palestinian investigators said the report showed Arafat did not die because of old age or ill health, but was the victim of an "assassination".
Israel's government has dismissed any suggestion that it was involved.
The Palestinian leader died in Paris, less than a month after being taken ill in the West Bank. His medical records said he had a stroke resulting from a blood disorder.
His widow, Suha, objected to a post-mortem at the time but agreed to allow Swiss, Russian and French experts to take samples from her late husband's remains last November after traces of polonium-210 were found on Arafat's personal effects in 2011.
At a news conference in the West Bank city of Ramallah on Friday, the head of the Palestinian committee, Tawfik Terawi, directly blamed Israel for Arafat's death.
"It is not important that I say here that he was killed by polonium,'' he said. "But I say, with all the details available about Yasser Arafat's death, that he was killed and that Israel killed him."
Mr Terawi did not present evidence of Israeli involvement, other than what he said were "statements by Israeli leaders who at the time said that Yasser Arafat should go, and should disappear".
"We say that Israel is the prime, fundamental and only suspect in the case of Yasser Arafat's assassination, and we will continue to carry out a thorough investigation to find out and confirm all the details and all elements of the case," he added.
It is not clear how the Palestinian investigators believe the poison was administered to Arafat, who was surrounded by guards and a close circle of aides at his Muqataa compound in Ramallah at the time.
The BBC's Yolande Knell, who was at Friday's hearing, said that in response to that question, Mr Terawi said he had "security information" but could not make it public.
Israel emphatically denied the allegations.
"I will state this as simply and clearly as I can: Israel did not kill Arafat, period. And that's all there is to it," Israeli Foreign Ministry spokesman Yigal Palmor told the BBC.
"The Palestinians need to stop levelling these accusations without a shadow of proof. Enough is enough."
Suha Arafat believes the findings prove her late husband was murdered, but says he had many enemies around the world and could not directly accuse anyone.
"I can't accuse anybody. Everybody wants to accuse Israel - I can't accuse - I can't jump into conclusion," she told the BBC.
She has called for an international inquiry, but Mr Terawi said that was a decision for the Palestinian Authority. The French authorities have opened a murder probe.
On Wednesday, al-Jazeera revealed the findings of 10 experts at the Vaudois University Hospital Centre (CHUV) in Lausanne, Switzerland.
"New toxicological and radio-toxicological investigations were performed, demonstrating unexpectedly high levels of polonium-210 and lead-210 activity in many of the analysed specimens" taken from Arafat's ribs, pelvis and soil that absorbed his bodily fluids, their report said.
Despite the lack of adequate biological samples and the long period between burial and the investigation, they concluded that the results "moderately support" the theory that Arafat's death was the consequence of poisoning with polonium-210.
The head of the Swiss team, Prof Francois Bochud, told reporters on Thursday: "Was polonium the cause of the death for certain? The answer is no, we cannot show categorically that hypothesis that the poisoning caused was this or that."
At Friday's news conference in Ramallah, the medical expert on the Palestinian committee quoted the separate report by the Russian Federal Medico-Biological Agency.
"The outcome of the comprehensive report on the levels of polonium-210 and the development of his illness does not give sufficient evidence to support the decision that polonium-210 caused acute radiation syndrome leading to death," said Dr Abdullah Bashir.
But Dr Bashir noted the Russian scientists had still found "large amounts" of polonium-210 in Arafat's remains, and said their report further "supports our theory" that he did not die of disease or old age, "but rather by poisonous material".