The two rivals for Ukraine's presidency failed to reach agreement at a meeting Friday, with the opposition leader demanding fresh elections.
The meeting, presided over by outgoing President Leonid Kuchma and attended by senior European envoys, saw no breakthrough between Prime Minister Viktor Yanukovich and opposition leader Viktor Yushchenko, the two key figures in the country's political crisis.
After the meeting, Yushchenko threatened to take action unless a rerun is held on Dec. 12.
"We will allow only a few days for the negotiation process," he said. "If Yanukovich wants to drag things out, we will take active measures, "Yushchenko told supporters in Kiev.
As the election crisis entered its fifth day, tens of thousands of supporters of Yushchenko took to the streets, demanding the overturn of official poll results and the installation of Yushchenko as president.
The election controversy is threatening to further divide the country, with Yushchenko calling for a nationwide strike.
"We are organizing citizens, stopping lessons at schools and universities, stopping work at enterprises, stopping transport... We'll force the authorities to think about what they are doing," said Oleksandr Moroz, Yushchenko's major ally.
Yushchenko enjoys strong backing in the west, a traditional stronghold of nationalism, while Yanukovich draws much support from the pro-Russian, heavily industrialized eastern half of the country.
Although Friday's talks produced no agreement, a multilateral working group had been established to find a solution to the crisis.
The meeting, also attended by Lithuanian President Valdas Adamkus, European Union foreign policy chief Javier Solana, Russian State Duma Chairman Boris Gryzlov, and Jan Kubis, head of the Organization for Security and Cooperation in Europe, was held amid growing signs that the dispute over Ukraine's seat of power widens the rift between Russia and the West.
On Friday, Russian Foreign Minister Sergei Lavrov accused Western countries of intervening in Ukraine's political crisis in an attempt to encourage the former Soviet republic to move toward the West.
Meanwhile, the European Union and the United States have backed Yushchenko and have refused to accept the election results.
Yanukovich and Yushchenko each won around 40 percent of the vote in the first round of the presidential election held on Oct. 31. The Central Election Commission on Wednesday declared Yanukovich the winner of a second round run-off.