Protesters in Ukraine seized a government building in the capital of Kiev on Friday, intensifying pressure on the government to call elections.
The siege continued after opposition leaders emerged in the morning following talks with President Viktor Yanukovych late on Thursday.
Senior opposition leader Oleh Tyahnybok called on demonstrators in Kiev to continue their truce for several more days, to which some demonstrators responded with chants of “revolution” and “shame”.
Mr Tyahnybok attempted to appease crowds by declaring that he had promised to stop further detentions of protesters and to ensure the release of dozens detained following clashes with police.
But other opposition leaders offered mixed reports on the outcome of the meeting, with Vitali Klitschko saying negotiations had achieved little. “The only thing we were able to achieve was not much,” he told the crowd.
He and Mr Tyahnybok were booed at the barricades by angry demonstrators and the atmosphere appeared tense.
President Yanukovych has called an emergency session of parliament next week to discuss the protests.
Interior Minister Vitali Zakharchenko issued a statement late on Thursday guaranteeing that police would not take action against the large protest camp on Independence Square, known as the Maidan. He also urged police not to react to provocations from demonstrators.
The protests have been largely peaceful, but turned violent on Sunday after Yanukovych pushed through harsh anti-protest laws and stonewalled protesters' demands that he call new elections.
Demonstrations began two months ago after President Yanukovych abruptly rejected an association agreement with the European Union in favour of a bailout loan from Russia. Two people were shot and killed in clashes on Wednesday, marking the first deaths since the protest began, and fuelling fears of further escalation.
One protester Andriy Moiseenko said of the seizure of the Ministry of Agricultural Policy: “We need to keep people warm in the frost. We cannot have people sleeping in tents all the time.”
The demonstrators have allowed ministry workers to take their possessions from the building, but have not allowed them to go to work.
The move followed the seizure of local governors' offices in several western regions on Thursday.
In Lviv, near the Polish border, 450 kilometers (280 miles) west of the capital, hundreds of activists burst into the office of the regional governor Oleh Salo, appointed by President Yanukovych, shouting “Revolution!” They forced a local governor to sign a resignation letter and remained in the building, stopping workers from entering.
Protesters have also retained control of offices in four other western cities seized Thursday, though they suffered a setback in Cherkasy, about 150 kilometers (90 miles) southeast of Kiev, where police barricaded the governor's building from inside and prevented them from taking control.
The opposition maintains that as many as five people died in Wednesday's clashes, though they say they have no evidence because the bodies were removed by authorities.
The interior ministry said yesterday that 73 people had been taken into custody, including 52 being investigated for “mass riots” - a new criminal charge that carries a prison sentence of up to eight years.
Reaction from the West and neighbouring Russia has been mixed.
On Friday, Germany and France summoned the Ukrainian ambassadors in their capitals to express their concern about the violent crackdown against anti-government protesters in Kiev.
The US has revoked the visas of Ukrainian officials linked to violence and threatened more sanctions.
On Thursday US Vice President Joe Biden called President Yanukovych and urged him to end the bloodshed.
EU Commission President Jose Manuel Barroso said that if the situation in Ukraine does not stabilise, the EU “would assess possible consequences in its relationship”.
Russia accused the West of meddling in Ukraine's affairs.
“We feel regret and indignation about the obvious foreign interference in the developments in Kiev,” President Vladimir Putin's spokesman, Dmitry Peskov, said.
Additional reporting by AP
See more incredible photos of the protests in Kiev below:
In pictures: Clashes between police and demonstrators in Kiev, Ukraine
In pictures: Clashes between police and demonstrators in Kiev, Ukraine
Anti-government protesters clash with police on Hrushevskoho Street in Ukraine's capital city on Friday night
Anti-government protesters attempt to take over the Ukrainian House on Sunday night
Protesters and police officers clash during the night of Friday to Saturday. After two months of primarily peaceful anti-government protests in the city center, new laws meant to end the protest movement have sparked violent clashes in recent days
Anti-government protesters clash with policemen in Kiev on Friday night as the protests continue in Ukraine
Anti-government protesters gather around a fire to get warm at a road block in Kiev on 26 January
An anti-government protester prepares to throw a Molotov cocktail during the clashes between protesters and policemen on 24 January
Anti-government protesters hurl Molotov cocktails and burn tires during clashes with police on Hrushevskoho Street near Dynamo stadium on January 24
Protesters confront police in central Kiev on Friday night
Anti-government protesters launches a firework towards police near the Dynamo Stadium in Kiev
Rob Stothard/Getty Images
A protester waves a Ukrainian flag during clashes with police in central Kiev
A protester throws a tire onto a fire in Kiev
Opposition leader and former WBC heavyweight boxing champion Vitali Klitschko addresses protesters near the burning barricades between police and protesters in central Kiev
A protester breaks up a mannequin on the roof of the burned truck during clashes with police in central Kiev
A protester throws tires onto a fire during a clash with police in central Kiev
Thick black smoke from burning tires engulfed parts of downtown Kiev as an ultimatum issued by the opposition to the president to call early election or face street rage was set to expire with no sign of a compromise
Protesters use a large slingshot to hurl a Molotov cocktail at police in central Kiev
Burning members of the Ukrainian riot police due to the gasoline bombs hurled by anti-government protestors during the clashes in central Kiev
A demonstrator holds an incendiary device as protesters clash with police in the center of Kiev
Protesters burn tires as they clash with riot police during an anti-government protest in downtown Kiev
Protesters clash with police in central Kiev. Police in Ukraine's capital tore down protester barricades and chased demonstrators away from the site of violent clashes, hours after two protesters died after being shot
A riot police officer escorts a man as a woman with a cross reacts nearby during clashes between police and pro-European protesters in Kiev
Riot policemen arrest a protestor during an anti-government protest in downtown Kiev
An injured man is escorted during clashes between police and pro-European protesters in Kiev
Medical workers help an injured man during anti-government protest in downtown Kiev
Medical personnel transport a man who was injured during clashes with riot police in Kiev
A man reacts after he was injured during a rally held by pro-European protesters in Kiev
An Orthodox priest tries to stop clash protesters the police in the center of Kiev
Ukrainian priests stand between protesters and riot police officers during an anti-government protest in downtown Kiev
An elderly woman walks from police officers as they block a street during unrest in central Kiev
An Ukrainian opposition activist speak to riot-forces standing guard in front of the parliament in Kiev
A protester smokes at the barricade in front of armour-clad security forces blocking access to the Verkhovna Rada parliament in Kiev
Pro-European protester take cover during clashes with riot police in Kiev. Two demonstrators were reported killed in new anti-government unrest in the Ukrainian capital, inflaming protesters who confronted police shouting 'Murderers' and 'Glory to Ukraine!'
Pro-European protesters launch a pyrotechnic pistol towards riot police during clashes in Kiev
A police officer throws a Molotov cocktail during clashes with protesters in central Kiev
A pro-European protester lies on the ground during clashes with riot police in Kiev
Demonstrators beat on a burnt vehicle as pro-European integration protesters hold a rally in Kiev
People stand on a barricade during a clashing break of the opposition and the police in Kiev
Protesters tip over a burnt out police bus during an anti-government protest in downtown Kiev
A pro-European protester fires a pneumatic gun during clashes with Ukrainian riot police in Kiev
Protesters wearing headbands reading 'Help' shout slogans during an action entitled 'Impose sanctions - stop the violence' in front of the European Union delegation in Ukraine in Kiev. Participants of the rally urged the European Union to immediately impose personal sanctions for those responsible for the use of force against peaceful protesters and journalists, as well as involved in the adoption of unconstitutional laws in Ukraine that violate fundamental human rights
A pro-European integration protester catches fire during clashes with police in Kiev
A pro-European integration protester sits in a burnt police bus after a rally near government administration buildings in Kiev
A pro-European integration protester uses a slingshot during clashes with police in Kiev
A bare chested man waves a Ukrainian flag during clashes between the opposition and police in the centre of Kiev. Opposition protesters were today locked in a tense standoff with Ukrainian police in Kiev after bloody clashes that wounded over 200 people, as President Viktor Yanukovych called emergency talks to resolve the crisis
A protester sprays fire in the direction of the riot police during clashes in the centre of Kiev. EU foreign ministers deplored violent protests in Kiev, saying the government was at fault for passing a package of repressive laws in an effort to tame pro-EU demonstrations
Pro-European integration protesters carry Molotov cocktails during clashes with police in Kiev. Protesters clashed with riot police in the Ukrainian capital after tough anti-protest legislation, which the political opposition says paves the way for a police state and was rushed through parliament
A protester prays as he holds an open Bible during an anti-government protest in downtown Kiev
Protesters clad in improvised protective gear prepare for a clash with police in central Kiev
Pro-European protesters bang on a metal bin during a rally in Kiev
A clergyman opposes riot police in Kiev during a rally held by pro-European integration demonstrators. Protesters gathered in Independence Square as repressive new laws came into force
Pro-European Union activists sing the national anthem in central Kiev