Election officials on Wednesday declared Prime Minister Viktor Yanukovych the winner of Ukraine's presidential election, prompting opposition leader Viktor Yushchenko to call for a nationwide strike to protest what his camp contends was brazen vote fraud.
"This decision puts Ukraine on the verge of civil conflict," Yushchenko said, calling for a transport stoppage and other strike action.
49.46 percent of Sunday's vote, against Viktor Yushchenko's 46.61 percent, the election commission said in announcing the final results.
Yushchenko called the commission's final count "their latest crime."
"With this decision, they want to put us on our knees," he told his followers massed in Independence Square, as the crowd chanted: "Shame! Shame!"
"My actions to combat the current regime will be even more consistent and powerful," Yushchenko pledged.
Earlier Wednesday, U.S. Secretary of State Colin Powell said the United States cannot accept the results of the elections "because it does not meet international standards and because there has not been an investigation of the numerous and credible reports of fraud and abuse."
Powell called "for a full review of the conduct of the election and the tallying of election results."
"If the Ukrainian government does not act immediately and responsibly, there will be consequences for our relationship," he added.
Powell said he spoke with outgoing Ukraine President Leonid Kuchma and urged that his government not crack down on demonstrators. He also spoke with other regional leaders, including Russian Foreign Minister Sergey Lavrov.
Powell did not elaborate about his conversation with Lavrov, but said he advocated a solution to the crisis in Ukraine that is "based on the law, using legal procedures."
The State Department confirmed Tuesday that it had summoned the Russian ambassador and discussed Ukraine. The Kremlin described the meeting as "unprecedented interference" in another country's affairs.