As he left the clinic where doctors made the diagnosis, Yushchenko said that he did not want to talk about the poisoning until after the Dec 26 rerun of the presidential runoff.

He thanked the medical staff that made the diagnosis. Doctors say it could have been fatal but Yushchenko's health is now improving and he's capable of returning to the campaign trail.

Yushchenko praised the thousands who staged street protests against the outcome of the presidential runoff election won by Prime Minister Viktor Yanukovych.

Ukrainian Presidential Candidate Viktor said: "I think that the heart of Ukraine moved to Independence Square in Kiev over the last three weeks and old people, young people, everyone were defending not Yushchenko but they were defending their choice for the type of Ukraine they want to see in the future."

Earlier on Saturday, several thousand people rallied in support of Viktor Yanukovich in the eastern city of Donetsk. The former prime minister said in a television interview that outside forces have financed Yushchenko's election campaign. And he denounced what he called "pressure" on the courts and on parliament, which dismissed him and called for the election rerun.

Meanwhile, Prime Minister Viktor Yanukovich has called for an investigation into whether the US helped finance Yushchenko's election campaign. He's asking the Supreme Council to set up a special committee to look into the matter.