Ukrainian opposition leader Viktor Yushchenko has called on a huge crowd of supporters to march to parliament, where an emergency session on Sunday's disputed presidential election is due to take place Tuesday.
Some 100,000 people gathered in Kiev for a second straight day to protest what they call widespread fraud in the run-off election.
Many protesters spent the night in freezing cold in the capital after Mr. Yushchenko called for peaceful protests until the results are overturned.
Protests are also under way in other cities, including Lviv, where at least 40,000 people have gathered to show opposition support.
Ukraine's election commission has yet to name a winner, but says Moscow-backed Prime Minister Viktor Yanukovych has a slim, but insurmountable lead.
The United States and other Western countries say there are indications of extensive voter fraud.
Information for this report is provided by AP, AFP and Reuters.