Ukrainian opposition leader and presidential candidate Viktor Yushchenko’s mysterious illness was caused by dioxin poisoning, doctors said Saturday.

“There is no doubt about the fact that Mr. Yushchenko’s disease has been caused by a case of poisoning by dioxin,” said Dr. Michael Zimpfer, director of Vienna’s private Rudolfinerhaus clinic.

Tests run over the past 24 hours provided conclusive evidence of the poisoning, Zimpfer said.

Physicians began running new tests Friday evening, when Yushchenko was admitted for a third time to the clinic, Zimpfer said.

“We started last night to do the entire imaging, including nuclear medicine, to look at the function of the organs, skeletal system and to see what kind of damage might be hiding,” he said.

Doctors also investigated Yushchenko’s blood to check for any signs of poisoning.

The illness has disfigured Yushchenko’s face, leaving it swollen, ashen and pockmarked.

The presidential candidate has accused Ukrainian authorities of trying to poison him ahead of last month’s vote - an allegation they have denied.

“I plan to live for a long time and I plan to live happily. I am getting better health every day,” he said.

Yushchenko, 50, first fell ill in September and was rushed to the Vienna hospital. He resumed campaigning later in the month but with a pockmarked and badly disfigured face.

His chief of staff, Oleh Rybachuk, told PBS’ “NewsHour with Jim Lehrer” that Yushchenko has fully recovered from his unidentified ailment but “needs a certain rest and he needs to take care of this effect on his face, which they call residual.”

“Internally there are no more damages,” Rybachuk said.

Rybachuk also said Yushchenko was fortunate to receive earlier treatment in Vienna.

“He was very lucky that he was brought to Vienna because doctors said if he would stay another 24 hours in Ukraine, it could be a ‘final solution,”’ he said in comments broadcast Friday.

Yushchenko suffered from a series of symptoms, including back pain, acute pancreatitis and nerve paralysis on the left side of his face.

If Yushchenko’s disfigurement turns out to be chloracne - a type of adult acne caused by exposure to toxic chemicals - it could take a long time to clear, Zimpfer said. Sometimes it takes two to three years for people to heal.

Ukraine’s Supreme Court voided the outcome of the November 21 presidential runoff election, which Yushchenko lost to Prime Minister Viktor Yanukovych, following allegations of massive vote fraud. A rerun of the ballot is slated for December 26.

Yushchenko told reporters in Vienna that he was confident of winning the election and that, in reality, he had already done so.