BBC News-The BBC's Steven Rosenberg saw the clashes unfold
Talks between Ukraine's government and opposition leaders are expected to begin on Monday following days of protests in the capital Kiev.
Parliamentary speaker Vlodymyr Rybak promised all sides would have an opportunity to express their opinions.
Protesters took to the streets over President Viktor Yanukovych's refusal to sign a deal on closer EU ties. They say they want him to resign.
Early on Monday, hundreds of activists were still occupying city hall in Kiev.
Thousands more spent the night in Independence Square.
Protesters stormed city hall on Sunday while a huge anti-government rally was taking place in the capital.
Between 100,000 and 500,000 took part in the rally, defying a ban imposed the day before.
There were also clashes near the presidential building on Sunday.
Masked demonstrators firing flares were driven back by riot police using tear gas, batons and stun grenades.
Dozens of protesters were injured and Kiev police said about 100 officers were wounded.
One group of protesters commandeered a bulldozer to try to break through police lines near President Yanukovych's headquarters.
Opposition leaders have called for a national strike and street protests to demand that the government resign.
Meanwhile, tents have been put up in Independence Square as protesters prepare for round-the-clock demonstrations.
"I, as the head of the Supreme Council, guarantee that literally tomorrow such a round table will take place and all representatives in this process will have an opportunity to express their opinions," Mr Rybak told Ukrainian TV.
The parliament speaker said President Yanukovych was "on the side of the people who are fully entitled to assemble for peaceful demonstrations and to express their views".
The leader of the opposition Fatherland party, Arseny Yatsenyuk, said the plan for Monday was to picket a meeting of the cabinet. He said a no-confidence motion had been submitted to parliament.
At city hall, members of the nationalist Svoboda party occupied the building and held meetings, Reuters reported.
The protesters chanted "Kiev is ours" and hung a Ukrainian flag in the window.
Opposition leader Vitali Klitschko - a former world boxing champion - urged supporters not to give up control of central Kiev overnight.
"We must mobilise everyone across the country and not lose the initiative," he said.
Protests started more than a week ago after President Yanukovych suspended preparations for signing an EU association agreement that would have opened borders to goods and set the stage for an easing of travel restrictions.
Mr Yanukovych argued that Ukraine could not afford to sacrifice trade with Russia, which opposed the deal.