Ukraine's parliament has adjourned a session on the disputed presidential poll, failing to pass a no-confidence motion in PM Viktor Yanukovych.
Several protesters managed to enter the parliament's lobby
Only 196 of the 410 MPs present backed the move.
The speaker of parliament said the session was getting too confrontational and would be resumed on Wednesday.
There were dramatic scenes as several protesters backing opposition leader Viktor Yushchenko - who says the poll was rigged - entered the parliament.
They broke through police cordons and into the parliament's lobby, shortly after lawmakers provisionally adopted a measure to annul Saturday's non-binding decision to declare the 21 November presidential run-off invalid. The protesters were later pushed back.
Trying to calm the situation, parliamentary speaker Volodymyr Lytvyn pledged that MPs would not repeal its previous decision.
Mr Yushchenko also urged protesters not to try to seize the parliament, described by some opposition leaders as the last "bastion of democracy".
The opposition's no-confidence motion called for a dismissal of the government to prevent anti-constitutional actions and separatism threatening the country's integrity.
A vote of no-confidence in the government would have no legal effect, but correspondents say it would be a big symbolic victory for Mr Yushchenko, a pro-Western liberal.
Meanwhile, the Supreme Court continues to hear opposition allegations of vote-rigging.
PM's offer rejected
The BBC's James Coomarasamy in the capital, Kiev, says the pressure seems to be mounting on Mr Yanukovych, widely seen as an ally of Russia.
POLITICAL CRISIS TIMELINE
21 Nov: Viktor Yanukovych declared winner of run-off poll
Independent observers declare the elections flawed, and thousands take to the streets
25 Nov: Supreme Court suspends publication of result until it considers the opposition's complaints
26 Nov: Mr Yanukovych and Mr Yushchenko hold talks and agree to seek peaceful solution
27 Nov: MPs declare election invalid, pass vote of no-confidence in the election commission
28 Nov: Eastern regions threaten to secede if Mr Yushchenko is declared president
29 Nov: Supreme Court meets to start considering complaints of poll abuses and arguments of pro-government camp
On Tuesday, Mr Yushchenko, a pro-Western liberal, rejected an offer by Mr Yanukovych to appoint him prime minister or for both men to withdraw from new elections.
The head of his electoral campaign has resigned and the outgoing President Leonid Kuchma, who backed Mr Yanukovych, has joined calls for fresh elections.
Mr Yanukovych said earlier he would agree to a partial re-run of the poll if there was evidence of mass violations.
The dispute has led to more than a week of mass protests by supporters of both Mr Yushchenko and Mr Yanukovych.
Mr Yushchenko accused his rival's negotiators of "sabotaging" talks aimed at resolving the crisis, and threatened to withdraw from them.
Mr Yanukovych's backers in eastern and southern regions of the country have threatened to demand autonomy if Mr Yushchenko becomes the new president of Ukraine.
But parliament in the Donetsk coal-mining region has now postponed an emergency session to discuss a referendum on autonomy.
In Moscow, an ally of President Vladimir Putin, parliamentary speaker Boris Gryzlov, warned that the situation in Ukraine "is heading towards a split or towards
The US and the European Union - who have refused to recognise the official results - have expressed concern about the possibility of Ukraine breaking up.
Mr Kuchma warned on Monday that the country's financial system faced collapse after reports from Ukraine's central bank that there had been a rush to withdraw bank deposits.
Last week, the Supreme Court suspended the official results, which saw Mr Yanukovych declared the winner with 49.46% of the vote to Mr Yushchenko's 46.61%.
Mr Yushchenko's team has submitted some 11,000 of allegations of ballot-rigging to regional courts and one complaint to the Supreme Court.
The government has also lodged 7,000 complaints of irregularities to regional courts.
Mr Yushchenko has declared himself the rightful winner, alleging massive fraud. His concerns have been echoed by international observers.
But the Supreme Court could take up to a week to reach a decision.
The court - seen as relatively independent - cannot invalidate the whole election, but it can uphold a complaint and order a partial or full recount.