Yushchenko ally Yuliya Timoshenko earlier today called on supporters to march peacefully on the president's headquarters.
Meanwhile, outgoing Ukrainian President Leonid Kuchma tonight insisted that all sides meet immediately to resolve the crisis, calling the ongoing mass protests a "political farce," according to Reuters.
"This political farce being played out now...is very dangerous and can lead to unforeseen consequences," Kuchma said in a statement read out by a newscaster on state television and quoted by Reuters. "I urge representatives of all political forces in Ukraine to sit down immediately at the negotiating table."
Kuchma, who effectively backed candidate and Prime Minister Viktor Yanukovych in the presidential race, vowed that authorities would not be the first to employ force. But he also indicated that they are "ready to uphold law and order."
Kuchma's office said earlier today that he cannot intervene in the results of the disputed presidential election.
Prime Minister Yanukovych went on television today to accuse the opposition of being radicals.
"A group of radicals has set itself the aim of splitting Ukraine by violence and illegal methods," Yanukovych said. "They are following a previously prepared scenario and are trying to drag in young people."
An estimated 200,000 Yushchenko supporters demonstrated today in central Kyiv, with many still gathered well into the evening despite the freezing temperatures, while tens of thousands protested in several other major cities.
Earlier today, Yushchenko took a symbolic oath of office on the floor of the parliament. Accusing the authorities of falsifying the election, he told supporters that he had acted in line with the real choice of the people. Yushchenko had wanted parliament to take up a nonbinding vote of no confidence in the Central Election Commission and call for official results showing his defeat to be nullified, but legislators could not muster a quorum.
Yushchenko also addressed demonstrators in central Kyiv early in the evening and called on civil servants to back his claim of victory.
Kyiv's city council and the administrations of four other large cities -- Lviv, Ternopil, Vinnytsia, and Ivano-Frankivsk -- have refused to recognize the official results and have backed Yushchenko, AP has reported.
A spokeswoman said the Central Election Commission will not release final results today.
Nearly complete official vote counts show Prime Minister Yanukovich leading by nearly three percentage points.
Today's related stories:
"Ukraine's Opposition Leader Urges Officials To Support Him"
"Protests Continue As Opposition Demonstrators Seek To Overturn Vote"
"Experts Ponder Possible Outcome Of Election Dispute"
"Ukraine: EU Criticizes Elections"