KIEV, Ukraine -- The Supreme Court ordered a rerun of the head-to-head presidential contest between Western-leaning Viktor Yushchenko and the Kremlin-backed candidate on Dec. 26, setting off rejoicing Friday by opposition supporters who waved orange flags and ignited fireworks as they chanted "Yushchenko! Yushchenko!"
The court found that government bodies had "illegally meddled in the election process" and distorted the results of the Nov. 21 runoff. The bold ruling was a rebuke to outgoing President Leonid Kuchma and Russian President Vladimir Putin.
Hundreds of thousands of Yushchenko followers celebrated in the capital, chanting his name, wearing orange headbands that said "YES!" and waving orange balloons. Passing cars blasted their horns three times to sound out the syllables in "Yush-chen-ko." The crowds were the largest in the 12 days since protesters set up their tent camp in Independence Square.
In pro-Moscow eastern Ukraine, supporters of Prime Minister Viktor Yanukovych expressed anger at the decision.
"We have a president -- Viktor Yanukovych," said Konstantin Sadalsky, shaking his fist at a TV screen in an Internet cafe in the eastern city of Donetsk.
Kuchma had initially supported Yanukovych and later -- under pressure from the throngs in Kiev and international monitors who called the vote fraudulent -- pushed for a completely new election. Critics said he hoped to field a new candidate more popular than Yanukovych.
The Supreme Court decision also was a slap at Putin, who appeared with Yanukovych during the campaign, congratulated Yanukovych on winning and on Thursday backed Kuchma's call for an entirely new vote involving all candidates.
The two-week standoff since the Central Election Commission declared Yanukovych the winner of the runoff led to the lowest point in Russia's relations with the West since the NATO bombing of Serbia in 1999. The decision by the 21 justices -- and a Yushchenko victory on Dec. 26 -- could drag this former Soviet republic of 48 million out of Moscow's orbit and generate pressure for greater democracy in Russia.
Ukraine's Parliament planned a marathon session this weekend to pass an election law for the Dec. 26 vote in hopes of preventing the kind of fraud that marred the first runoff. Lawmakers were also expected to consider the opposition's demands to replace the 15-member election commission.
"We have proven that we are a nation that could defend our choice," Yushchenko, wearing an orange scarf, told supporters in Independence Square. "Justice and freedom are coming back to Ukraine thanks to you, real heroes."
The crowd, which steadily grew after the court decision, chanted "Yushchenko! Yushchenko!" during his pauses, and he responded by blowing kisses. Then the throng struck up the national anthem.
Yushchenko's appeal to the court had pointed to evidence of rampant fraud in eastern regions near the border with Russia, where Yanukovych got most of his votes. Among other irregularities, the court found that voter rolls were tampered with and people voted more than once.
Yanukovych's representative in court, Stepan Havrysh, said the verdict was a "political decision" that wasn't backed by evidence. "The court yielded to pressure and was driven by emotions," Havrysh said.
White House spokesman Scott McClellan called the ruling "an important step in moving toward a peaceful, democratic resolution that reflects the will of the people."
"What is important now is to move ahead quickly, as called for by the Supreme Court, to ensure a new vote that is fair, free and that results in an outcome that reflects the will of the Ukrainian people," State Department spokesman Richard Boucher said.
Poland's president and other European leaders also welcomed the decision.
Putin, who has been angered by Western denunciations of the election, delivered what appeared to be a stinging criticism of Washington on Friday for seeking a "dictatorship of international affairs" -- though he did not specifically mention the United States.
"Even if dictatorship is wrapped up in a beautiful package of pseudo-democratic phraseology, it will not be in a position to solve systemic problems," Russia's Itar-Tass news agency quoted him as saying in a speech in New Delhi, India.
In Independence Square, people shouted approval as Yushchenko, a former prime minister and central bank chairman, urged Kuchma to fire Yanukovych immediately and called for disbanding the election commission.
"Find the courage to do that -- stop tormenting the nation," Yushchenko said.
He said the election commission had "betrayed" the nation by endorsing a fraudulent vote.
Yushchenko urged his supporters to keep up the pressure on the government and not to drop their demonstration in the square. "After such a holiday, I'm asking you not to leave," he said.
The Supreme Court's ruling came after dark, more than six hours after the judges went into their chambers.
Convoys of opposition reinforcements clad in orange -- Yushchenko's campaign color -- had crowded the capital ahead of the ruling. "This is the only decision we have been waiting for," said Anatoly, a 56-year-old engineer.
The ruling is final and cannot be appealed, and the repeat vote is to be held nationwide, rather than only in the districts specifically challenged by Yushchenko.
Ivan Kuras, Yanukovych's ally in parliament, said the prime minister could withdraw from the race, the Interfax news agency reported. Havrysh said he didn't know whether Yanukovych would run, but said he could still win.
According to Ukrainian law, if one of two rivals in the runoff steps down more than 10 days before the vote, a first-round contender who came in third is put on the ballot. If Yanukovych leaves the race, socialist leader Oleksandr Moroz, who had thrown his support behind Yushchenko in the Nov. 21 runoff, would take his place.
If Yanukovych withdraws less than 10 days before the vote, the law would require Yushchenko to get more than 50 percent of the vote to win the presidency.
The Donetsk region in eastern Ukraine has already set a January referendum seeking a measure of autonomy, and Havrysh warned that the Supreme Court's verdict could foment unrest there.
"This decision may entail serious social and political consequences in eastern Ukraine," Havrysh said. "The people on Kiev streets have pressed their demands home, but people on Donetsk streets could also do that. The rerun will undoubtedly lead to a split in Ukrainian society."
In Kiev, Yushchenko supporters appeared confident.
"I hope he will win the revote, provided there are no more falsifications," said Lena Marunich, 41, as she danced to Yushchenko's campaign song -- "Together We Are Many and We Cannot Be Overcome" -- played from the stage at Independence Square.