The United States has welcomed Ukraine's decision to invalidate the results of a disputed presidential runoff election.
White House spokesman Scott McClellan called Friday's court ruling an important step toward a peaceful, democratic resolution that reflects the will of the people.
Meanwhile, two top European officials are returning to Ukraine to help mediate the dispute.
The Organization for Security and Cooperation in Europe says its secretary general, Jan Kubis, will make his third such visit to Ukraine in a week, beginning Friday.
The OSCE says Mr. Kubis will seek ways the 55-nation group can help resolve Ukraine's political situation.
Lithuanian President Valdas Adamkus will also visit, for the third time in 10 days.
Earlier, Russia's lower house of parliament accused Western European institutions of aggravating tensions over the election.
Some information for this report provided by AFP and Reuters.