JERUSALEM — The discovery of traces of a radioactive agent on clothing reportedly worn by Yasser Arafat in his final days reignited a cauldron of conspiracy theories Wednesday about the mysterious death of the longtime Palestinian leader.

Arafat’s widow, who ordered the tests by a Swiss lab, called for her husband’s body to be exhumed, and Arafat’s successor gave tentative approval for an autopsy. But experts warned that even after the detection of polonium-210, getting answers on the cause of death will be tough.

Arafat was 75 when he died Nov. 11, 2004, in a French military hospital. He had been airlifted to the facility just weeks earlier with a mysterious illness, after being confined by Israel for three years to his West Bank headquarters.

At the time, French doctors said Arafat died of a massive stroke. According to French medical records, he had suffered inflammation, jaundice and a blood condition known as disseminated intravascular coagulation, or DIC.

But the records were inconclusive about what brought about the DIC, which has numerous causes including infections, colitis and liver disease. Outside experts who reviewed the records on behalf of The Associated Press were also unable to pinpoint the underlying cause.

The uncertainty sparked speculation about the cause of death, including the possibility of AIDS or poisoning. Many in the Arab world believe he was killed by Israel, which held him responsible for the bloody Palestinian uprising of the early 2000s. Israeli officials have repeatedly denied foul play, and they dismissed the latest theories as nonsense.

That debate was reignited after a Swiss lab said Wednesday it had discovered traces of polonium-210 in clothing and other belongings provided by Arafat’s wife, Suha. She told the lab that Arafat had used the items in his final days. The development was first reported by the Al-Jazeera satellite channel.

In an interview Wednesday in Doha, Qatar, Mrs. Arafat said she was pleased to be getting closer to determining the cause of her husband’s death.

“I was shocked first, of course, because it’s a very dangerous poison that ... they discovered,” she told APTN. “But I was relieved that we are on the steps of knowing the truth.”

She strongly hinted that she thinks Israel, which is widely believed to have a nuclear weapons program, was responsible, but stopped short of openly saying so.

“Not the whole world has access to nuclear elements. We have to make a more profound and deep investigation to know all the truth about his death,” she said.

Polonium-210 is best known for causing the death of Alexander Litvinenko, a one-time KGB agent turned critic of the Russian government, in London in 2006. Litvinenko drank tea laced with the substance.

Francois Bochud, who heads the Institute of Radiation Physics in Lausanne, Switzerland, told the AP on Wednesday that his lab had discovered “very small” quantities of polonium-210, which is naturally present in the environment. But levels found in blood and urine samples taken from the clothing were well above normal.

Bochud said an “elevated” level of more than 100 millibecquerel, a measurement of radioactivity, was found on Arafat’s belongings. That’s compared with levels of some 10 millibecquerel in some control samples.

He said Arafat’s wife told him she had stored the items in her lawyer’s office after her husband died. It was not clear why she waited so long to test them.

Bochud stressed that the discovery did not provide proof that Arafat had been poisoned. That would require further testing.

“What is possible to say is that we have an unexplained level of polonium, so this clearly goes toward the hypothesis of a poisoning, but our results are clearly not a proof of any poisoning,” he said by telephone from Switzerland.

In the West Bank, Arafat’s successor, President Mahmoud Abbas, cleared the way for an autopsy.

“The Palestinian Authority was and remains fully prepared to cooperate and to provide all the facilities needed to reveal the real causes that led to the death of the late president,” Abbas’ office said in a statement. “There are no religious or political reasons that preclude research on this issue, including an examination of the remains of the late president by a reliable national medical body, upon request and approval by his family.”

The top Muslim cleric in the Palestinian territories, Mufti Mohammed Hussein, also gave the green light to help allay possible objections in the conservative Muslim society.

With Mrs. Arafat and religious authorities in agreement, it was unclear what other steps were needed for the body to be exhumed from his mausoleum-style burial site in the West Bank town of Ramallah.

Palestinian officials have long argued that Israel had the means and motive to kill Arafat, whom it accused of encouraging suicide bombings and shootings that claimed hundreds of Israeli lives during the uprising. While confining Arafat to his West Bank headquarters, Israel tightly controlled everything going in and out of the compound.

Palestinian official Saeb Erekat on Wednesday called for an international investigation into Arafat’s death.

In Israel, officials dismissed the renewed speculation.

“Making up conspiracy theories based on pretend evidence is so ludicrous that it befits the comedy channel and not a news channel,” said Foreign Ministry spokesman Yigal Palmor. “If there is anything suspicious about his death, then the French doctors would have known and said something.”

Dov Weisglass, the chief of staff of Israel’s then-Prime Minister Ariel Sharon, insisted in a radio interview that Israeli officials never considered killing Arafat. In fact, he said, Sharon opposed the idea because he feared that it could spark widespread violence.

Sharon “didn’t think his (Arafat’s) physical liquidation would help. On the contrary,” Weisglass told the Army Radio station.

Denis Gutierrez, a senior French military doctor, said he did not know whether French medics checked Arafat for polonium-210 while he was at France’s Percy military hospital. And Gutierrez was unaware of any mention of poisoning in the 558-page classified report on Arafat’s death.

But Gutierrez said nothing was sent from the hospital to the Swiss lab, raising questions about the belongings that were tested. “Samples taken in the hospital remain in the hospital,” he said.

Experts said Arafat’s remains would have to be tested to know more.

“You don’t know much about the provenance of the clothing and whether it had been tampered with later on. You’d want to test the body,” said Alastair Hay, a professor of environmental toxicology at the University of Leeds in England.

Other signs seemed to speak against the possibility of radioactive poisoning.

Hay said hair loss or damage to bone marrow would be key signs of poisoning.

But Buchod said Arafat’s medical records said his bone marrow was in good shape and he didn’t lose his hair, unlike Litvinenko.

Also, Arafat’s condition in the French hospital briefly improved before sharply deteriorating in his final days. Such improvement might contradict poisoning as a cause.

A 2007 study by radiation experts from Britain’s Health Protection Agency concluded that once Polonium-210 is deposited in the bloodstream, its potent effects are nearly impossible to stop. A poisoning victim would experience multiple organ failure as alpha radiation particles bombard the liver, kidneys and bone marrow from within.

Polonium-210 breaks down relatively quickly. The isotope has a half-life of 138 days — the time it takes for half of the sample to decay. Experts were divided over whether a reliable sample could even be salvaged.

“Eight years after the event, it’s a very long time. I doubt that you’d get much polonium-210,” said Chris Lloyd, a British government radiation protection expert.

Derek Hill, an expert on radiological science at King’s College London, said it would still be possible to detect polonium in Arafat’s corpse, despite the length of time since his death.

“It would still be a lot higher than the naturally occurring, very low, background level, so you would still be able to detect that he had polonium in his body, I would say, with a pretty high confidence,” Hill said.

One key question is where the polonium-210 might have come from.

John Croft, a retired British radiation expert who worked for the British agency during the Litvinenko crisis, said a dose large enough to kill would likely have to come from a government with either civilian or military nuclear capabilities. That could point to Israel, which has a nuclear research program, but also include dozens of other nations.

“You would need to have access to very sophisticated facilities,” he said.