Ukraine's justice minister is threatening to call for a state of emergency after demonstrators occupied the Justice Ministry and protests demanding the president's resignation spread.

Tensions remained high in Kiev on Monday as several dozen protesters from a group named Spilna Sprava (The Right Deed) seized control of the ministry building late on Sunday, smashing windows and erecting barricades outside.

Justice Minister Olena Lukash, who is taking part in negotiations between the opposition and President Viktor Yanukovich, said she would ask for the talks to be broken off if the building was not freed.

"I will be forced to ask the president of Ukraine to stop the talks if the building is not freed immediately and negotiators are not given a chance to find a peaceful solution to the conflict," Lukash told Ukraine's Inter channel.

If the protesters do not vacate the building, Lukash said she would also approach Ukraine's national security council with "a demand to discuss imposing a state of emergency in this country".

She did not specify a deadline for leaving.

Opposition leaders said reconciliatory gesture from Yanukovich was not enough to end the ex-Soviet country's worst crisis since independence and demanded snap elections this year.

Protests spreading

The protests began more than two months ago over Yanukovich's rejection of a pact with the European Union under Russian pressure.

But they have now turned into an all-out bid to oust him from power.

Protesters have already attempted to blockade 14 of the 25 regional administrations, including in southern and eastern parts of the nation of 46 million that predominantly speak Russian and share an historical allegiance to Moscow.

The EU has urged dialogue between the two sides, a call echoed by Pope Francis, who voiced hope in his weekly Angelus prayer that "the search for common good may prevail in the hearts of all".

Under unprecedented pressure, Yanukovich on Saturday offered the opposition posts in government including that of prime minister, but his opponents said the offer fell short of their needs.

Yanukovich proposed sharing leadership with Fatherland party chief Arseniy Yatsenyuk as prime minister and UDAR (Punch) chief and former boxing champion Vitaly Klitschko as deputy prime minister.

Klitschko, who is believed to have a personal rivalry with Yatsenyuk, condemned the proposal in an interview with German newspaper Bild am Sonntag.

"This was a poisoned offer by Yanukovich designed to split our opposition movement," he was quoted as saying.

Opposition leaders have been careful, however, to neither accept nor explicitly reject Yanukovich's proposals.