The Ukrainian government has canceled a planned meeting at its headquarters in Kiev after hundreds of protesters massed outside to prevent Prime Minister Viktor Yanukovych from entering.
Government officials told reporters Wednesday the cabinet meeting would not take place, as planned. No explanation was given.
Earlier, opposition leader Viktor Yushchenko, the apparent winner of Sunday's presidential runoff election, urged supporters to stage a blockade to stop Mr. Yanukovych from convening the meeting.
Meanwhile, officials say Mr. Yanukovych has filed a formal complaint with the Central Election Commission challenging Sunday's runoff, claiming widespread fraud.
Official results show Mr. Yushchenko won 52 percent of the vote.