VIENNA, Austria – Ukrainian presidential hopeful Viktor Yushchenko was poisoned with dioxin, most likely intentionally, doctors in Vienna who have been struggling to diagnose his mystery illness confirmed Saturday.

Yushchenko, a pro-Western opposition leader engaged in a bitter presidential contest, has alleged since suddenly falling ill in September that he was poisoned in an assassination attempt. Authorities have denied the charge, and some government supporters have ridiculed it.

Michael Zimpfer, director of the private Rudolfinerhaus clinic that has been treating Yushchenko, said tests prove that dioxin caused the illness that has disfigured the Ukrainian candidate’s face.

“There is no doubt about the fact that Mr. Yushchenko’s disease has been caused by dioxin poisoning,” he said. The doctors, Zimpfer said, “suspect the involvement of an external party,” and that damage to Yushchenko’s digestive system suggested the dioxin was given orally.

The diagnosis was based on clinical observations, skin changes and findings from tissue and blood samples, he said.

Asked whether he had reported his findings to the Ukrainian authorities, Zimpfer replied that Austrian justice officials have been in direct contact with Ukraine since Yushchenko’s second hospitalization in late September.

Yushchenko fell sick Sept. 6, the day after having late-night food and drinks with the head of the Security Service of Ukraine, among other people.

Yushchenko has suffered problems that affected several internal organs and caused severe back pain, according to his doctors. The most visible symptom has been disfigurement of his face with pockmarks, cysts and darkened areas.

The findings could have an unpredictable effect on a repeat presidential runoff election pitting Yushchenko against Prime Minister Viktor Yanukovych on Dec. 26. The revote was set after the Supreme Court ruled the Nov. 21 balloting, narrowly won by Yanukovych, invalid because of fraud.

Speaking to a rally in the eastern city of Luhansk before the Vienna announcement, Yanukovych expressed sympathy for Yushchenko. “As for the reasons,” he said, “I know nothing. Let the specialists work on that.”

Yushchenko first checked into the Vienna clinic Sept. 10. Yushchenko’s dioxin levels in blood and tissue samples taken in September but only recently tested specifically for that substance were at least 1,000 times higher than normal.

Zimpfer said that Yushchenko’s dioxin levels have returned to normal and that he probably would leave the clinic today or Monday.

Nikolai Korpan, the doctor who oversaw Yushchenko’s treatment, said no “functional damage” would remain as a result of the dioxin exposure. But the doctors said that Yushchenko’s facial disfigurement would remain for a long time as follow-up treatments continue.

Associated Press

Dioxin poisoning changed Viktor Yushchenko’s appearance dramatically between the summer (left) and Friday (right).