Doctors in Vienna say Ukraine's opposition leader Viktor Yushchenko was the victim of dioxin poisoning.

The director of a leading Vienna hospital, Rudolfinerhaus - Dr. Michael Zimpfer, told reporters there is no doubt the illness that disfigured Mr. Yushchenko's face was the result of the dioxin.

He said blood tests and a check on the size and functioning of Mr. Yushchenko's vital organs confirmed the poisoning. But he stressed that it remains unclear if it was deliberate.

Mr. Yushchenko became ill in September. He has consistently accused Ukrainian authorities of trying to poison him in the run-up to November's disputed presidential election.

Ukraine's Supreme Court voided the outcome on grounds of widespread fraud. According to those results, Prime Minister Viktor Yanukovych won the vote.

Court ordered repeat of the runoff balloting is set for December 26.