Tymoshenko's team complained Sunday that pro-Yanukovich forces were buying votes and engaging in multiple voting in his stronghold of eastern Ukraine. They also complained that one of their poll managers was "murdered" Sunday morning, and a safe full of ballot papers stolen.
They also suggested they might challenge the election's validity in the courts, because of a law passed last week that changed rules for how the country's 33,000 polling stations certify their vote counts.
"Because of that law, many regions of Ukraine were completely closed to public control," over the vote counting, says Viktor Nebozhenko, director of the Ukrainian Barometer, an independent Kiev think tank. "Democracy has lost in Ukraine."
After the exit poll results appeared, Tymoshenko campaign chief Oleksander Turchynov warned that it was too early to say anything for sure.
"The result of the majority of exit polls are within the margin of statistical error," he told journalists "Conclusions about who the victor is can be made only on the basis of the real results of the Central Election Commission."
Ukraine's politics have been stormy since the three weeks of rolling street demonstrations in 2004 that overturned Yanukovich's allegedly fraud-tainted win and led to the election of Viktor Yushchenko in a fresh election.
The incumbent Mr. Yushchenko, who was knocked out in the election's first round with a humiliating 5.4 percent of the votes, told journalists Sunday that the choice between Yanukovich and his Orange rival Tymoshenko was a "shame."