Germany and France summoned their Ukrainian ambassadors to express concerns about a violent crackdown against anti-government protesters in Kiev.

German Foreign Ministry spokesman Martin Schaefer said that the deaths of protesters in recent days "show how serious the situation is."

French Foreign Minister Laurent said there was "condemnation from France" of the escalating situation in Ukraine.

In Kiev, protesters seized the Ministry of Agricultural Policy while also maintaining the siege of several governors' offices in the country's west.

After meeting President Viktor Yanukovych on Thursday, opposition leaders told the crowds of protesters that he had promised to ensure the release of dozens of people who had been detained after clashes with police and to stop further detentions.

They urged the protesters to maintain the shaky truce following violent street battles in the capital, but were booed by demonstrators eager to resume their attacks on police.

Emerging from the hours-long talks with President Yanukovych, opposition leader Oleh Tyahnybok - a toxic racist who in April 2005 co-signed an open letter to former president Yushchenko calling for a parliamentary investigation into the "criminal activities of organised Jewry in Ukraine," - asked demonstrators for several more days to continue peace talks.

But other opposition leaders offered mixed reports on the outcome of the meeting, with Vitali Klitschko saying negotiations had achieved little.

Another opposition leader, Arseniy Yatsenyuk, said after the talks that "there was a really good chance" of stopping the bloodshed, but Mr Klitschko was more downbeat.

"The only thing we were able to achieve was not much," he told the crowd.

He urged protesters to refrain from violence and continue peaceful protests to avoid further bloodshed.

"I am afraid, yes, I am afraid of human losses," Mr Klitschko said.

"We will be widening the territory of the Maidan further until these guys start reckoning with us."

He and Mr Tyanhnybok were both booed at the barricades by angry demonstrators.

Protests have been centred on Kiev's main square, known locally as the Maidan.