Ukraine opposition urges fresh polls amid pro-EU rallies
Opposition parties in Ukraine have called for early elections amid ongoing protests at the government's refusal to sign an EU association agreement.
A "national resistance" HQ is to be set up, they said, followed by a nationwide strike. Thousands have regrouped in Kiev after being violently dispersed.
President Viktor Yanukovych said he was "deeply outraged" by the violence.
A big rally is expected on Sunday. Jailed ex-PM Yulia Tymoshenko has urged people to overthrow the government.
Ukraine refused to sign the EU deal after apparent pressure from Russia.
At the end of a summit in the Lithuanian capital on Friday, EU leaders warned they would not tolerate Russian interference in the bloc's relations with former Soviet republics.
The summit reached provisional accords with Georgia and Moldova.
Several Western countries condemned Saturday morning's intervention to disperse protesters gathered in Independence Square, which saw a number of people hurt.
Police said they had decided to clear Independence Square after "a number of incidents", Interfax Ukraine news agency reported. It was not clear what incidents they were referring to.
"It was horrible. We were holding a peaceful demonstration and they attacked us," said protester Lada Tromada. "They threw us away like garbage."
One activist, opposition MP Andriy Shevchenko, said at least 33 people were taken into police custody.
US state department spokeswoman Jen Psaki condemned "the violence by government authorities against peaceful demonstrators".
In a statement, she said: "We urge Ukraine's leaders to respect their people's right to freedom of expression and assembly. These are fundamental to a healthy democracy and the respect for universal values on which the United States's partnership with Ukraine depends."
For his part, President Yanukovych said in a statement: "I am deeply outraged by events that took place on Independence Square overnight. I condemn the actions which led to a confrontation and people suffering."
He vowed that those responsible for the use of force would be punished, but did not apportion blame.
Members of Ukraine's political opposition met for emergency talks after the dispersal.
"We have made a joint decision to form a national resistance taskforce and have begun preparing for an all-Ukrainian national strike," former Economy Minister Arseniy Yatsenyuk told reporters.
"Our demands are the resignation of [Interior Minister Vitali] Zakharchenko, an investigation of his actions and his trial, the resignation of the government and the president and early presidential and parliamentary polls.
"We... are calling on all civic activists, civil society and all those who care about Ukraine's future to fight the Viktor Yanukovych regime together."
A big rally has been announced for Sunday.
Ms Tymoshenko has urged protesters not to give in "until the regime is overthrown by peaceful means".
In a message read by her daughter, Ms Tymoshenko urged Ukrainians: "Fly, drive, walk to Kiev from all parts of Ukraine, but gather everyone on 1 December."
Last week, President Yanukovych said he was suspending preparations for signing an EU association agreement that would have opened borders to goods and set the stage for an easing of travel restrictions.
He said pressure from Russia had led him to make his decision. Mr Yanukovych argued that Ukraine could not afford to sacrifice trade with Russia, which opposed the deal.
EU Council President Herman Van Rompuy said the parties had been "really close" to signing the association agreement in Vilnius, but added: "We need to overcome pressure from abroad."
German Chancellor Angela Merkel said the door would always remain open for Ukraine.
Independence Square was the scene of the Orange Revolution in 2004, which saw Mr Yanukovych ousted and a Western-leaning government brought to power.
Mr Yanukovych was elected president five years later, narrowly defeating then-Prime Minister Tymoshenko, a leading figure of the Orange Revolution.
In 2011 she was sentenced to seven years in jail for abuse of office - a case widely criticised in the West as political revenge.
Ms Tymoshenko has been on hunger strike since Monday over the failure to sign the EU agreement.