VIENNA, Dec 11: The man who hopes to become Ukraine's next president was the victim of poisoning by dioxin - a toxic chemical that can easily be administered in soup containing cream, Austrian doctors said on Saturday.

Viktor Yushchenko, who faces Prime Minister Viktor Yanukovich later this month in a re-run of last month's rigged presidential election, long alleged he was poisoned as part of a plot to kill him.

His illness kept him out of the early stages of the election campaign in the former Soviet republic and left his face bloated and pock-marked.

"There is no doubt," Dr Michael Zimpfer, president of the Rudolfinerhaus clinic where Mr Yushchenko is undergoing treatment, Said at a news conference. "There were high concentrations of dioxin, most likely orally administered."

He said dioxin was very soluble and spreads quickly through the body once administered.

"We suspect a cause triggered by a third party," Dr Zimpfer said, though he added it was impossible to determine exactly how the poisoning took place.

"We weren't there and we will leave that to the legal authorities to decide," he added.

Mr Yushchenko arrived at the clinic on Friday evening and was to undergo further testing over the weekend.

DISFIGURING CONDITION: Medical experts have said Mr Yushchenko's disfiguring condition appeared to be "chloracne", commonly associated with dioxin poisoning.

Chloracne is a skin condition, similar to acne, that is caused by exposure to toxic chemicals such as dioxins. It usually results from occupational exposure to compounds in fungicides, insecticides and herbicides.

In anticipation of the announcement, Mr Yushchenko's U.S.-born wife, Kateryna, told reporters on Thursday she was certain the doctors would confirm her belief her husband was poisoned.

Mr Yushchenko says after attempting to poison him, his enemies used fraud to try to steal the run-off vote on Nov 21, in which Mr Yanukovich, backed by giant neighbour Russia, was declared winner.

The Supreme Court struck down the result on grounds of irregularities and ordered a new vote on Dec 26.

Mr Yushchenko told reporters on Friday his health was improving and he was optimistic he would win the re-run.

"Everything is going well," he told reporters outside the clinic, his wife acting as interpreter. "I plan to live for a very long time. I plan to be very happy. I am gaining better health every day."

Earlier in the week, he said it was his "growing conviction that what happened to me was an act of political reprisal against a politician in opposition. The aim, naturally, was to kill me." -Reuters