Opposition candidate Viktor Yushchenko hailed the ruling as "the beginning" of victory.
Prime Minister Viktor Yanukovych, the officially declared winner of the election, repeated a call for talks with his rival. He said the crisis could not be resolved "by ultimatums and pressure"
Tens of thousands of Ukrainians have massed in the center of the city today despite blustery winds and freezing temperatures to support Yushchenko and challenge the conduct and tally of the runoff.
Numerous demonstrators had spent another night camping out in tents pitched in downtown Kyiv to protest the alleged voter fraud.
Overnight, small groups of Yanukovych supporters also demonstrated in the streets of the capital. Both sides appeared to be trying to avoid open confrontation, with no incidents of major violence reported.
Police and the military protected the president's office and the election headquarters overnight, but otherwise police and security forces appear to be keeping a low profile.
In the western city of Lviv, an opposition stronghold, the speaker of the Lviv regional assembly declared Yushchenko the legitimate president of Ukraine. Mikhail Sendak said today that authorities in the region will only obey orders from Yushchenko and called on other regions to follow suit.
Countering The Opposition
Supporters of Yanukovych also launched counter rallies today in Kyiv.
Outgoing President Leonid Kuchma, who supports Yanukovych, has spoken of the risk of Ukraine toppling into civil war over the disputed presidential election.
In a speech shown on state television yesterday, Kuchma accused Ukraine's private Channel 5 television station of helping to prepare an overthrow of the government by giving broad coverage of the protests.
"The leadership of the country, security specialists, warned us that the provocative broadcasts of so-called objective news on Channel 5 prepared the ground for a coup d'etat, irrespective of the outcome of the election," Kuchma said.
Kuchma also said that he had asked both Yanukovych and Yushchenko to hold talks to defuse tensions, and he appealed to the international community to refrain from direct interference in Ukraine's internal affairs.
He said there had been appeals from what he called Ukraine's strategic partners "to re-examine the outcome of the election campaign" -- an apparent reference to Western calls for an inquiry into the conduct of the election.
Opposition Urges General Strike
Yesterday's call by Yushchenko and the opposition for a general strike to protest the vote tally appears to have had little impact in the capital Kyiv.
"A path to a compromise through people demonstrating their will is the only path that will help us find a way out of this conflict," Yushchenko told a rally after the official results were released yesterday. "Therefore, the committee of national salvation declares a nationwide political strike."
But teachers in Lviv went on strike as thousands of students boycotted classes, apparently to protest the election.
At a Russian-European Union summit in the Netherlands today, Russian President Vladimir Putin and EU officials discussed the Ukrainian election. Jan-Peter Balkenende, the Dutch prime minister who headed the EU side, said the polls had not been "free and fair." Putin said the elections had taken place in accordance with Ukrainian law and urged other governments not to interfere.
Former Polish President and Nobel Peace Prize winner Lech Walesa was in Kyiv today. Addressing Yushchenko supporters he said: "All my life I fought for the same ideals. Our situation was difficult, or perhaps more difficult than yours. I am amazed with your emotions and your enthusiasm. It is my firm belief that it will lead to your victory."
In Germany, Foreign Minister Joschka Fischer today called for the Ukrainian election to be examined under international supervision.
The United States and NATO have also urged authorities to review the runoff vote, which international monitors have criticized as fraudulent.
The Ukrainian Election Commission announced yesterday that Moscow-backed Yanukovych had won the runoff by roughly three percentage points, a figure that contrasted starkly with several exit polls that suggested Yushchenko won the vote.
(from RFE/RL and wire reports)
[To see RFE/RL's continuing coverage of "Ukraine's Contested Election," click here.]