KIEV, Ukraine - Ukraine's opposition leader and his American-born wife led tens of thousands of supporters in a march on parliament today to demand the government annul the results of the country's contested presidential election.

The Ukrainian Election Commission's announcement that Kremlin-backed Prime Minister Viktor Yanukovych was ahead of Western-leaning candidate Viktor Yushchenko with nearly all the votes counted dismayed - and angered - many of the former Soviet republic's 48 million people.

Yushchenko on Tuesday claimed victory and asked for international recognition. He also announced a campaign of civil disobedience and alleged official fraud.

"We appeal to the parliaments and nations of the world to bolster the will of the Ukrainian people, to support their aspiration to return to democracy," a statement from Yuschenko's campaign office said.

He called on an estimated crowd of 200,000 supporters camped at the central Independence Square to walk to the parliament building ahead of an emergency session called to consider both annulling the official results and a no-confidence vote in the election commission.

Shortly thereafter, Yushchenko and his American-born wife, Kateryna Chumachenko, led the throng toward parliament.

While such a parliamentary decision would carry huge political significance, it would not be binding. According to the Ukrainian constitution, a no-confidence vote must be initiated by the president in order for it to be binding. Outgoing President Leonid Kuchma has staunchly backed Yanukovych.

If the parliament doesn't take action to solve the crisis, "we will have no choice but to block roads, airports, seize city halls," said Yuliya Tymoshenko, a prominent opposition leader and Yushchenko's ally.

Special forces were deployed near the Central Election Commission, the presidential administration and other government buildings, but police stayed away from the protesters jamming the city's main avenue for a second day. The supporters clogged the city and turned sidewalks into seas of orange, Yushchenko's campaign color.

Although official results, with more than 99 percent of precincts counted, showed Yanukovych leading with 49.42 percent to his challenger's 46.70 percent, several exit polls had found Yushchenko the winner, one by a margin of 11 percentage points.

Russian President Vladimir Putin sent a statement to Yanukovych late Monday to congratulate him, but a group of international observers described Sunday's balloting as severely flawed.

Senator Richard Lugar, chairman of the U.S. Senate's Foreign Relations Committee, said in Kiev that there had been "a concerted and forceful program of election-day fraud and abuse." He called on Kuchma "to review all of this and take decisive action in the best interests of the country."

The European Union also called for an urgent review of the results and said Ukrainian ambassadors in member states would be briefed about its "serious concerns."