Ukraine's political opposition has said it will call a country-wide general strike to force the resignation of the country's president after police broke up pro-Europe protests using batons and stun grenades.

Arseny Yatsenyuk, one of three opposition leaders and a former economy minister, said on Saturday that the organisers have begun preparations for "an all-Ukraine national strike" to topple President Viktor Yanukovich.

"Millions of Ukrainians must rise up. The main thing is not to leave the squares until the authorities have been overthrown by peaceful means," Yulia Tymoshenko, jailed former prime minister, said in a letter read to journalists by her daughter.

The move came as around 100 Ukrainian protesters took refuge from police batons and biting cold inside the walls of a central Kiev monastery.

"This is the only safe place we have left, and besides I have nowhere else to go," said Alexander Ananich, a 17-year-old student from the city of Lviv.

Violent crackdown

The main protest, on Kiev's central Independence Square, swelled on Friday evening to nearly 10,000 people as news spread of Yanukovich's decision to orient Ukraine back towards former Soviet parton Russia by refusing to sign a key European trade deal at a Vilnius summit.

In the early hours of Saturday, police used batons and stun grenades to disperse the protest.

TV footage showed police beating one young woman on the legs and kicking young men on the ground. Several people were given emergency treatment on the spot for cuts to the head.

There were no hard figures on how many people were hurt.

"By my count we are talking of tens of cruelly beaten people, perhaps hundreds," Andriy Shevchenko, an opposition deputy, was quoted as saying by Interfax news agency. "It was absolute savagery."

The Interior Ministry said the riot police moved in "after the protesters began to resist the (ordinary uniformed) police, throwing trash, glasses, bottles of water and flares at them".

Police cleared away anti-Yanukovich posters and political graffiti and took down flags and banners, including the EU blue and gold standard, before sealing off the area.

The protests evoked memories of the "Orange Revolution" of 2004-5 against sleaze and election fraud, which doomed Yanukovich's first bid for the presidency. But those protests took place peacefully without police action and Saturday's violence was unprecedented in Kiev.

"There is a concern that these protests could grow into something resembling the Orange Revolution," in which Yanukovich was forced from office in 2004, said Al Jazeera's David Chater, reporting from Kiev.

"We are likely to see confrontation rather than compromise," in coming days, he added.