Opposition officials say they have cut off negotiations with the government aimed at settling the country’s bitter and divisive presidential election dispute.
Opposition leader Viktor Yushchenko rejected a power-sharing proposal put forward by Prime Minister Viktor Yanukovich.
Under the deal, Mr Yushchenko would become prime minister, and the constitution would be changed to transfer some of the president’s powers to the prime minister.
Mr Yanukovich has said he would accept a new vote if allegations of fraud are proven, but he also wants new candidates, meaning he and Mr Yushchenko would not run again in a new poll.
“That is stupidity. They’re trying to prolong the agony,” said Mr Yushchenko’s press secretary.
“The name ‘Yushchenko’ and the word democracy are synonymous for many people in the Ukraine.”
The behind-the-scenes talks have been progressing alongside parliamentary debates and the Supreme Court’s consideration of opposition charges of widespread electoral fraud.
The crisis has brought hundreds of thousands of demonstrators to Kiev, where Yushchenko supporters have blocked government buildings for several days.
Opposition leaders say the demonstrations will continue until their demands are met.
The east-west standoff over Ukraine continues to harden.
EU foreign policy chief Javier Solana has arrived in Kiev in an effort to mediate.
He will be joined by Polish President Alexander Kwasniewski and Lithuanian President Valdas Adamkus.
While Russian President Vladimir Putin is sending his envoy Boris Gryzlov, warning against “foreign pressure” in defusing the crisis.
Earlier Tuesday, Ukraine’s parliament failed to pass a motion of no confidence in the government.
The decision prompted a number of opposition protesters to break through a gate at the parliament building and try to storm the session.
The incident was over quickly, and protesters — some crawling on top of each other’s shoulders — only getting as far as the lobby before being pushed back by police.
With Western observers saying the election did not meet acceptable standards of fairness, the United States and Europe have refused to recognize the results.
Meanwhile, the threat of Ukraine splitting appears to have dissipated after the eastern Donetsk region backed down from a threat to hold a referendum on self-rule.