Hundreds of protesters have clashed with riot police in the centre of the Ukrainian capital Kiev, after the passage of harsh anti-protest laws seen as part of attempts to quash anti-government demonstrations.
A group of radical activists began attacking riot police with sticks, trying to push their way toward the Ukrainian parliament building, which has been cordoned off by rows of police and buses.
The protesters, many wearing hard hats and gas masks, used stun grenades and fire extinguishers and threw flares as they attacked police in riot gear. Numerous explosions were heard and plumes of smoke rose above the crowd. Activists chanted "Shame!" and "Revolution." Some were injured and medics were seen treating them.
Opposition leader Vitali Klitschko tried to stop the protesters from attacking police, but himself came under attack.
The clashes occurred shortly after a large peaceful rally on Kiev's main square, part of the anti-government protests rocking Ukraine since President Viktor Yanukovych's decision to freeze ties with the European Union and embrace Russia instead. Since then, Moscow has promised a 15 billion dollar (£9bn) bailout loan to aid Ukraine's struggling economy.
Scores of opposition leaders and journalists have been attacked, harassed and prosecuted, since the protests started on November 21.
Last week, Mr Yanukovych caused uproar at home and abroad when he approved a number of laws that limit Ukrainians' rights to protest, civic activism and free speech. The US called that legislation "undemocratic".
The laws prohibit demonstrators from wearing masks or hard hats at rallies, prompting many to don theatrical masks and kitchen pots at today's rally. Several opposition leaders addressed the crowds from a giant stage, wearing bright construction workers' hats. Other provisions of the controversial legislation restrict the activity of non-governmental groups funded by the West and seek to equate critical reporting with defamation.
Opposition leaders denounced Mr Yanukovych's legislation as unconstitutional and called for formation of parallel governing structures in the country.
"The power in Ukraine belongs to the people," said Arseniy Yatsenyuk, one of the several protest leaders.
Mr Yanukovych's government has ignored previous demands of the opposition.