EXPERTS trying to figure out why Ukrainian opposition leader Viktor Yushchenko fell seriously ill during the country’s presidential campaign are testing a number of poisoning theories but have no conclusive evidence he was poisoned, doctors said today.

It is still not known what caused the illness that struck Ukrainian opposition presidential candidate Viktor Yushchenko during the election campaign, leaving his face scarred, the director of the hospital that treated him said today.

AS Ukraine’s popular pro-western opposition leader laid claim to victory Tuesday in hotly contested presidential elections, the mystery surrounding an appearance-altering illness, that twice prompted him to check into a Vienna hospital, persisted.

International experts will help investigate whether a Ukrainian presidential candidate was poisoned by toxins normally found in biological weapons, Austrian doctors treating him said tonight.