Kiev, Ukraine ? Outgoing President Leonid Kuchma called for negotiations in Ukraine’s spiraling political crisis Tuesday, hours after the leader of the opposition declared himself the winner of a disputed presidential election.

The proposal for negotiations between the candidates — Kuchma-supported Prime Minister Viktor Yanukovych and the Western-leaning reformer Viktor Yushchenko — was out of character for the president, who is not known for compromising. But neither side held a clear advantage, and both had much to lose if violence should break out.

Earlier in the day, Yushchenko threatened a campaign of civil disobedience to back the opposition’s charge that authorities rigged Sunday’s vote in favor of Yanukovych.

“Ukraine is on the threshold of a civil conflict,” Yushchenko told lawmakers gathered for an emergency session. “We have two choices: Either the answer will be given by the parliament, or the streets will give an answer.”

As snow fell Tuesday night, more than 10,000 Yushchenko supporters marched to the presidential administration building, skirting some heavy trucks that blocked the street and facing off with hundreds of police in riot gear.

After a few hours, many demonstrators headed home, while some went back to a tent city set up on Kiev’s main avenue and Independence Square, where they pledged to stay until Yushchenko is declared president.

Yanukovych supporters early today were building their own encampment at a stadium several blocks from the opposition site.

The proximity of opposing sides raised new prospects of confrontation.

Kuchma’s statement, which was read on state television, referred to the demonstrations as a “political farce” that is “extremely dangerous and may lead to unforeseeable consequences.”

Also Tuesday, the European Union stepped up pressure on Ukraine to review the outcome of its disputed presidential election, which has triggered widespread criticism from across the continent.

Dutch Prime Minister Jan Peter Balkenende, speaking on behalf of the 25-nation body, called Kuchma, to say he doubted the outcome “reflected the will of the Ukrainian electorate.”

Senior officials across Europe voiced further criticism, and Ukrainian ambassadors were being summoned for talks in several capitals.