Ukraine's pro-Western presidential candidate has called for mass protests after official returns show the pro-Russian prime minister with an all-but unassailable lead in the hotly-contested presidential run-off. A joint observer mission representing the Organization for Security and Cooperation in Europe, the Council of Europe, the European Parliament and NATO said they had seen abuse of state resources in favor of Prime Minister Viktor Yanukovich.
Opposition leader Viktor Yushchenko called on his supporters Monday to "defend this victory" in the streets, as the vote count continued in Ukraine's capital city Kiev. He called the official count a fraud, and appealed to the European Union to put pressure on the government to concede defeat in Sunday's pivotal election.
The opposition leader alleges that fraud took place in eastern Ukraine, which is heavily populated by Russian speakers and where Mr. Yanukovich has his base of support.
The opposition leader says turnout figures of 96 percent in that region appeared inflated, and he charges that buses transported many voters to different locales in order for them to vote more than once.
International election monitors also reported widespread irregularities during Sunday's vote.
Various exit polls late Sunday night indicated that Mr. Yushchenko enjoyed a substantial lead. However a spokesman for Mr. Yanukovich dismissed the opposition's claims, saying the exit polls were "inaccurate and unrealistic."
Tens of thousands of Mr. Yushchenko's supporters gathered in central Kiev Sunday evening and again Monday morning, to protest alleged ballot fraud after the preliminary results showing Prime Minister Yanukovich in the lead.
The election is considered one of the most important in the former Soviet Union since the collapse of communism in 1991.
Observers say the choice is whether the country of nearly 50-million people moves closer to Europe politically or remains firmly in Russia's orbit.
Russian President Vladimir Putin made two unprecedented trips to Ukraine during the election campaign to all but endorse Mr. Yanukovich, who heads one of the country's largest business clans and wants to make Russian a second language.
Mr. Yanukovich is also the chosen successor to outgoing President Leonid Kuchma, whose 10-year rule has been marked by allegations of human rights abuses and corruption.
The United States and European Union have warned Ukrainian authorities that "there will be consequences" if the election is not seen as being free and fair.