Doctors treating former Russian prime minister Yegor Gaidar believe he was poisoned, an aide said Thursday.

Gaidar, a liberal opposition leader who served briefly as prime minister in the 1990s under President Boris Yeltsin, began vomiting and fainted during a conference in Ireland on Nov. 24 — the day after former Russian spy Alexander Litvinenko died in London after a suspected poisoning.

Gaidar, 50, was first taken to an intensive care unit at an Irish hospital and is now recovering in a Moscow hospital. His aide says he's feeling better.

"Doctors don't see a natural reason for the poisoning and they have not been able to detect any natural substance known to them" in Gaidar's body, spokesman Valery Natarov said.

"So obviously we're talking about poisoning (and) it was not natural poisoning."

Doctors in Ireland initially suspected Gaidar's diabetes or some sort of ailment caused his illness.

Gaidar's daughter, Maria, said President Vladimir Putin called her father on the phone to inquire about his health and wish him a smooth recovery.

Anatoly Chubais, a top Yeltsin-era government official, said he suspects a link between Gaidar's illness, Litvinenko's death and last month's murder of Russian investigative reporter Anna Politkovskaya. High doses of polonium-210, a rare and radioactive element, were found in Litvinenko's body.

Daughter doesn't suspect Putin

Gaidar's daughter, Maria, is more critical of the Kremlin than her father. She ruled out that suggestions that Putin or his government were involved. She said it could have been masterminded by forces seeking to discredit Putin.

"It could have been (in the) interest ... (of) some people who are fighting against Putin and who want destabilization in the country," she told the British Broadcasting Corporation.

Gaidar is a liberal economist whose criticism of the Kremlin is largely limited to economic issues. He's one of the leaders of a liberal political party, but he is not prominent because liberals have been severely sidelined under Putin.

Gaidar is unpopular among many Russians. They blame the liberal, Western-backed economic policies he pursued as prime minister for the decline in their living standards following the Soviet collapse.