Yushchenko returned home to campaign for this month?ˉs presidential runoff vote. He said he did not want the poisoning issue to overshadow the Dec. 26 election, but the director of Vienna?ˉs elite Rudolfiner clinic said a potential criminal case could be involved.

?°We are not dealing with simple pimples, we are dealing with a poisoning and the suspicion of third-party involvement,?±Dr. Michael Zimpfer said, referring to the disfigurement of Yushchenko?ˉs face.

Clinic doctors said it took a newly developed test, conducted by a lab in Amsterdam, Netherlands, to determine beyond doubt that dioxin poisoning caused Yushchenko?ˉs mystery illness in September, leaving him disfigured and in pain.

Whoever was responsible may have thought dioxin was untraceable, Zimpfer said.

Yushchenko said he expected an investigation to find the culprits, but he urged that it be conducted after the runoff to avoid influencing the results.

Ukraine?ˉs prosecutor general?ˉs office said it reopened the criminal investigation it closed in November for lack of evidence. Yushchenko fell ill Sept. 5 and was treated at the Vienna clinic twice before.

Lawmakers from Yushchenko?ˉs party said the clinic findings confirmed that opponents wanted to assassinate or disable the Western-leaning politician rather than take the risk he would defeat Prime Minister Viktor Yanukovich in the presidential election.

Yanukovich campaigners rejected suggestions the Kremlin-backed prime minister was involved in a poisoning attempt. There is ?°no logic in such an accusation,?±said Taras Chornovyl, Yanukovych?ˉs campaign manager.

Also Sunday, Yanukovich?ˉs spokesman, Oleh Ternovsky, said the prime minister wanted Ukraine?ˉs parliament to investigate whether the United States helped finance Yushchenko?ˉs campaign.

Washington has spent more than US$65 million in the past two years to aid political organizations in Ukraine, but U.S. officials say no American funds were sent directly to political parties.