Earlier today, Ukraine's Central Election Commission said that with 99 percent of the ballots counted, Yanukovych was leading with 49 percent of the vote compared to just under 47 percent for his rival Viktor Yushchenko.
Yushchenko has refused to accept the results.
Election observers from the East and the West are also at odds over the official numbers. Monitors from the CIS hailed the poll as democratic.
But the head of the U.S. team of observers in Kyiv, Senator Richard Lugar, had harsh words for the Ukrainian authorities in the wake of the poll.
"It is now apparent that a concerted and forceful program of election-day fraud and abuse was enacted with either the leadership or cooperation of government authorities," Lugar said.'Disturbing Patterns Of Abuse'
Monitors from the Organization for Security and Cooperation in Europe (OSCE), the Council of Europe, and other foreign groups also said the election failed to meet international standards.
The United States said today that the runoff was marred by disturbing patterns of abuse.
State Department spokesman Adam Ereli told reporters that unless the deficiencies are resolved in the postelection period, Washington may take action against those who participated in vote fraud. He did not elaborate.
Ereli said charges of voting irregularities need to be thoroughly investigated and cleared up before the international community can have confidence that the election results reflect the will of the people.
Ukraine's security agencies are warning tonight they will crush any street violence triggered by the disputed poll.
The prosecutor-general, the Interior Ministry, and the security services issued the statement as an estimated 100,000 protesters
jammed the main square in Kyiv.
Yushchenko told the crowd that he had no confidence in the official vote count, giving Yanukovych an unassailable lead. He called for parliament to be summoned.
(RFE/RL/Agencies)See also: Amid Protests, Both Candidates Claim Ukraine Election Victory