Ukraine challenger in strike call
Powell warns leaders to rethink or face 'consequences'
Yuschenko speaks to supporters in central Kiev Wednesday.
The U.S. has a significant stake in what is happening in Ukraine.
Ukraine demonstrators brave the snow to show their support for the opposition leader.
CNN's David Ensor looks at possible consequences of the election crisis.
KIEV, Ukraine (CNN) -- Ukraine's Liberal opposition challenger Viktor Yushchenko has said he does not recognize the election of Ukraine's prime minister as president and has called for a country-wide "political strike."
The country's election commission has declared PM Viktor Yanukovych the winner of a hotly contested presidential runoff, but U.S. Secretary of State Colin Powell quickly dismissed the contest as marred by fraud.
Speaking in Washington, Powell urged Ukraine's leaders to "respond immediately" warning "there will be consequences" for the United States' relationship with Ukraine. (Full story)
"This decision puts Ukraine on the verge of civil conflict," Yushchenko told tens of thousands of supporters massed in Kiev's main square for the third straight day, calling for a transport stoppage and other strike action.
Olexander Moroz, Socialist Party leader, said the opposition wanted to halt transport and close factories and schools but said the crisis could be resolved by holding new elections.
Yanukovych meanwhile described himself as the head of state on Wednesday and proposed immediate talks with liberal challenger Yushchenko.
"We must improve our lives and we will do it together -- all of our citizens and myself as president of Ukraine...," Yanukovych said in a brief appearance on state television monitored by Reuters.
"Tomorrow, we start talks with Yushchenko's team. We will look for common ground. I am ready to listen to the opposition proposals."
Pro-Moscow Yanukovych had 49.46 percent of the vote while Yushchenko was named on 46.61 of the ballots, the commission said Wednesday.
The final official results failed to disperse the thousands of Yushchenko supporters who have packed the capital's Independence Square for the past three days in freezing temperatures and blowing snow, hoping to hear that their man would win.
Singers continued to perform on a stage, and orange banners and flags, the color of the opposition party, waved above the hat-covered heads of the protesters.
A small group of pro-government marchers rallied around the Central Election Commission's imposing white limestone building, waving blue and white flags in support of Yanukovych.
Ukraine's outgoing president has offered to hold talks to end the crisis, but a Yushchenko ally said the only thing to discuss was a transfer of power to the opposition leader.
President Leonid Kuchma called for negotiations late Tuesday, saying the opposition's actions amounted to a "political farce" that could lead to "serious consequences," according to news reports.
He said Ukraine faced the threat of civil war and urged the world community not to interfere in the row.
Addressing a meeting of regional leaders, shown on state television, Kuchma referred to the civil war which followed the 1917 Bolshevik revolution and said this "could well become a reality at the present time."
He said he had asked both Yanukovich and Yushchenko to hold talks "and asked the world community to refrain from direct interference in Ukraine's internal affairs." (Full story)
Kuchma said authorities would not be the first to use force but would uphold law and order.
In an interview with CNN's Jill Dougherty ahead of the commission's announcement, Yuschenko called the results "fraudulent" but promised there would be no violence from the thousands of demonstrators in Kiev's main square. (Full story)
Yuschenko then told supporters he was prepared to rerun the election provided it was overseen by honest officials.
Should Ukraine's parliament pass a no-confidence vote against the election commission, the matter would go to the Supreme Court, which could then annul the vote in some areas, including some in which as much as 95 percent of the vote was reported cast for Yanukovych.
CNN's Jill Dougherty and Ryan Chilcote contributed to this report.