"Evidence of American support (for Yushchenko) has surfaced more than once. Therefore, Yanukovych is asking for a parliamentary investigation," said Yanukovych's spokesman, Oleh Ternovsky.

Ukraine was plunged into a political turmoil after the presidential runoff on Nov. 21, when both candidates claimed victory.

Ukraine's Supreme Court on Dec. 3 annulled the official resultsof the runoff, with Yanukovych being the winner and ruled that a re-run would be held on Dec. 26.

It was reported that the US Bush administration has spent more than 65 million US dollars in the past two years to aid political organizations in Ukraine.

US officials say the activities do not amount to interference in Ukraine's election but are part of the 1 billion dollars the US State Department spends each year trying to build democracy worldwide. They say no American funds were sent directly to Ukrainian political parties.

Yanukovych has often accused the United States of meddling in Ukraine's internal affairs.

Meanwhile, Yushchenko, who is popular in the West, called for an investigation to determine how he was poisoned by dioxin, but said it should be conducted after the Dec. 26 re-run to avoid influencing the results.

Doctors at a Vienna clinic in Austria said tests proved beyond doubt that it was dioxin poisoning that caused a mystery illness in September that left Yushchenko disfigured and in pain.

After the diagnosis, Ukraine's prosecutor general's office said it had reopened the criminal investigation that it closed in November for lack of evidence at the time.

Yanukovych campaigners rejected suggestions that the prime minister could have been involved in poisoning Yushchenko.

There is "no logic in such an accusation," said Taras Chornovyl, Yanukovych's campaign manager.

Yushchenko fell ill on Sept. 5 and has been treated at the Vienna clinic twice before.

Hospital director Michael Zimpfer said Yushchenko's blood contained more than 1,000 times the normal amount of dioxin. He said tests showed the toxin was taken orally.

Dioxin is a byproduct of industrial processes such as waste incineration and chemical and pesticide manufacturing.