KIEV, Ukraine - Tens of thousands of supporters of opposition candidate Viktor Yushchenko demonstrated in Ukraine's capital for a third day today, while an ally of the presidential aspirant said the only thing to negotiate with authorities was the transfer of power.

Yushchenko on Tuesday claimed victory over the Kremlin-backed prime minister, Viktor Yanukovych, in Sunday's presidential run-off, which many Western nations said did not meet democratic standards. While nearly complete election results have put the Kremlin-backed candidate ahead, exit polls showed Yushchenko won.

Outgoing President Leonid Kuchma late Tuesday called for talks involving all sides.

But today, Mykola Tomenko, a lawmaker and Yushchenko ally, told a crowd of supporters - awash with Yushchenko's orange campaign color - that the opposition would only discuss Yushchenko's accepting power.

"We are ready to negotiate only about the peaceful handing over of power to Yushchenko by Kuchma," Mykola Tomenko, a lawmaker and Yushchenko ally, told a crowd of supporters who maintained their vigil on the capital's central Independence Square and the adjacent main avenue.

Opposition supporters have taken over blocks of Kiev's main street, setting up a giant tent camp. There has been a near total absence of police officers, although as the supporters marched to the presidential administration building on Tuesday they met phalanxes of riot police outside. The stand-off ended without incident.

Supporters of Yanukovych, who has the Kremlin's backing, have become increasingly visible in Kiev, setting up hundreds of tents on a wooded slope less than half a mile from the opposition's even larger tent camp.

Mykola, a miner from Kriviy Rih in eastern Ukraine, said that he came to the capital to prevent "usurping power."

"We have no one to bring us food and clothes as our opponents (do)," he said, referring to the huge outpouring of support from Kiev residents for the Yushchenko supporters camping in the cold. "But we will win because we believe in Ukraine."

Official results released by the Central Election Commission, with more than 99.48 percent of precincts counted, put Yanukovych ahead with 49.39 percent of the votes to his challenger's 46.71 percent. But several exit polls indicated Yushchenko was the winner.

The European Union today stepped up pressure for the election result to be reviewed. Western observers have said it was seriously flawed.

European Commission President Jose Manuel Barroso warned today of "consequences" for political and trade relations with Ukraine if the government doesn't allow a full review of the election.

But Russian President Vladimir Putin, visiting Portugal on Tuesday, branded the observers' criticism "inadmissible" as there are still no complete official results. Ukraine "doesn't need to be lectured," he said through an interpreter.