PARIS — Yasser Arafat, hospitalized in France with a mystery ailment, was rushed to intensive care after suffering a setback and was undergoing a new round of tests, Palestinian officials said early Thursday.

The two officials, speaking on condition of anonymity, said the 75-year-old Arafat's condition had seriously deteriorated over the past day, adding that doctors who have been examining him since Friday still don't know the cause of his illness.

French hospital and military officials refused to comment, but more information was expected from a previously planned news conference this afternoon.

Meanwhile, Arafat's top aides denied there had been any setback and accused Israel of spreading rumors. The report first aired on Israel's Channel Two television.

"These unfounded reports are not coming from French medical teams. These are leaks from the Israeli side," said Mohammed Dahlan, a former Palestinian security chief.

"Leaking such rumors will only complicate things and also complicate the situation within the Palestinian public," he told reporters in Paris.

Haled Salem, Arafat's top aide, said early Thursday that the medical analysis was "deepening a little bit" but he remained confident Arafat would recover. "There are no setbacks."

Arafat, who has been ill for three weeks, was flown to the French military hospital on Friday after passing out briefly at his West Bank headquarters in Ramallah.

He was initially said to be suffering a bad case of flu, with symptoms of vomiting and diarrhea. Doctors later found so-far-unexplained blood and digestive abnormalities.

Palestinian officials insist publicly that leukemia or any other form of cancer, as well as any type of poisoning, had been ruled out.

Undoubtedly conscious of the anxiety at home about the possible death of Arafat, who has led the Palestinians for 40 years without grooming an obvious successor, Palestinian aides had previously said he was improving and undergoing further tests.

In Israel, speculation has ranged from a viral infection to stomach cancer.

His brother, Fathi Arafat, is hospitalized in Cairo, Egypt, with an advanced stomach cancer, according to doctors there.

On Wednesday, Arafat spokeswoman Leila Shahid said he felt well enough to ask about the U.S. presidential election. An aide later issued a statement in Arafat's name congratulating President Bush on his re-election.

Israeli Foreign Minister Silvan Shalom said Israel is tracking Arafat's health "very carefully.

"Our goal is to prepare for the day after, if and when he dies," he told Israel Radio.

Israeli intelligence was widely criticized after it was caught off guard last week by the sudden deterioration in Arafat's health.

Shalom said Arafat's condition "is very serious," but gave no details. At the same time, he said, "it is too soon to eulogize Yasser Arafat."