As the opposition vowed to block the country's roads, airports and railways in response to a nationwide strike call by the opposition leader Viktor Yushchenko who refused to recognise the officially declared win of his rival, Prime Minister Viktor Yanukovic.
Yushchenko said he did not recognise Yanukovic's election as president, accusing officials of widespread fraud and called for a country-wide "political strike".
"We do not recognise the election as officially declared," Yushchenko told tens of thousands of supporters massed in Kiev's main square for the third straight day.
He said the proclamation of results giving victory to Yanukovic put Ukraine "on the brink of civil conflict".
Outgoing President Leonid Kuchma warned that the crisis could turn violent. "[Civil war] could well become a reality at the present time," he said.
In an attempt to defuse the situation, Yanukovic, after his declaration as the new president, on Wednesday said his team would enter into negotiations with opposition leader Yushchenko's camp.
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.
Yushchenko called on supporters
to stage a national strike
"The committee of national salvation announces a political strike in the whole of Ukraine," Yushchenko said to roaring cheers from the crowd.
"We are going to look for a solution in an open battle. The government wants an escalation of the conflict; it has rejected political dialogue," he said.
Yushchenko contends that the government helped rig Sunday's presidential election in favour of his opponent and said the election commission's announcement amounted to a "state coup d'etat".
He spoke a few hours after the election commission said with ballots from all polling stations counted, Yanukovic received 49.46% of the vote, compared to 46.61% for Yushchenko, a difference of nearly one million votes.
"We are going to look for a solution in an open battle"
The election has split Ukraine in two, with the nationalist Ukrainian-speaking west supporting Yushchenko and the industrialised Russian-speaking east backing Yanukovic.
It has also exposed a Cold War-like rift between Russia - which backs Yanukovic and says the election was fair - and much of the West, which has said it was riddled with fraud.
In Washington, the United States on Wednesday rejected the results of the election, calling for a review of the tally.
"We cannot accept this result as legitimate, because it does not meet international standards and because there has not been an investigation of the numerous and credible reports of fraud and abuse," US Secretary of State Colin Powell said.
"We call for a full review of the conduct of the election and the tallying of election results," Powell said, adding there was still time to correct the result without violence.
Powell says US rejects results of
the Ukrainian election
"It is still not too late for authorities to find a solution that respects the will of the Ukrainian people," he said.
"We're not looking for a contest with the Russians over this," he said. "We're looking for a way to make sure that the will of the Ukrainian people is respected."
Asked if Russia had unduly influenced the result in favour of Yanukovic, Powell said: "We do not believe we have seen that in this instance."