Here in Washington, officials are closely following developments in Ukraine with measured optimism about mediation efforts by Poland and the European Union. They have again urged restraint by security forces and political protestors.

Though Washington is on a semi-holiday footing on the day after Thanksgiving, Secretary of State Colin Powell, his deputy Richard Armitage and other top officials are at work and monitoring developments in Ukraine.

An official here said the United States, while taking a low public profile on the issue, is supporting efforts by Poland and the European Union to try to mediate between the rival political camps in Ukraine.

He said the United States is urging continued restraint by political demonstrators in Kiev and Ukrainian government security forces, and is trying to do what it can to support a resolution of the standoff consistent with Ukrainian law.

The official expressed cautious optimism about signs of compromise in the political dialogue and said the important thing is to get the parties talking about how to peacefully deal with widespread concerns about the conduct of last week's election.

U.S. Ambassador to Ukraine John Herbst is said to be in continuing touch with aides to Ukrainian President Leonid Kuchma and representatives of the election rivals, Prime Minister Viktor Yanukovych and former Prime Minister Viktor Yushchenko.

Secretary of State Powell discussed the situation by telephone Thursday with German Foreign Minister Joschka Fischer and Dutch Foreign Minister Bernard Bot, who briefed Mr. Powell on Thursday's summit between the European Union and Russia at the Hague.

The United States has criticized Moscow for its early embrace of Mr. Yanukovych as the election winner despite the fraud charges, though Mr. Powell said Wednesday the United States is not  "looking for a contest" with Russia over the issue.

There has been no formal U.S. statement on Ukraine since Wednesday, when Mr. Powell said the United States could not accept the announced result of the election, a victory for Mr. Yanukovych, because of what he said were "extensive and credible" reports of fraud.

He called for a full review of the conduct of the election and the tallying of results and said it was not too late to find a solution that respects the will of the Ukrainian people.

At the same time, he said there would be "consequences" for U.S.-Ukrainian relations, and for Ukraine's hopes for Euro-Atlantic integration, if the Kiev government did not act immediately and responsibly to address the concerns.

The State Department issued an alert late Thursday urging U.S. citizens to defer non-essential travel to Ukraine, particularly to Kiev, because of the potential for civil unrest and disturbances in the aftermath of the disputed election.