Activists have clashed with riot police in the the Ukrainian capital Kiev over a controversial law that upgrades the status of the Russian language and which critics say would undermine the Ukrainian tongue.
The bill leaves Ukrainian as the only state language, but allows the use of Russian in Russian-speaking regions in courts, education and other government institutions.
Members of the pro-Western opposition say the bill would effectively smother the Ukrainian tongue by removing any incentive for millions of Russian-speaking Ukrainians to learn and speak it. They also say it would bring Ukraine back into the Russian orbit and torpedo its efforts to forge closer ties with the European Union.
MPs loyal to president Viktor Yanukovych, who draws his support from the Russian-speaking east and south, rushed the bill through parliament on Tuesday night, without giving the opposition much chance to debate and protest over it.
Parliament speaker Volodymyr Lytvyn insisted the vote was illegitimate and announced his resignation, along with a deputy parliament speaker. Seven national MPs announced a hunger strike.
"I have been fooled, Ukraine has been fooled, the people have been fooled," Mr Lytvyn.
Up to 2,000 protesters staged an angry protest against the bill outside a government building in the centre of Kiev. Riot police moved in after the activists attempted to block the entrance to the building. Protesters hurled bottles of water and sticks at the police and both sides used pepper-spray against each other.
Ambulances rushed to the scene to treat protesters and police who were injured in the clashes. Vitali Klitschko, the WBC heavyweight champion and also an opposition leader, was injured and had blood streaming from his hand.
Mr Yanukovych's critics accuse him of using the contentious language issue to win back support from his Russian-speaking constituency ahead of the October parliamentary elections as his approval ratings slide amid economic hardships. They say he is using the controversy to divert attention from the politically tainted imprisonment of former premier Yulia Tymoshenko and other top opposition leaders, which has drawn a storm of anger from the West.
An earlier debate of the bill in parliament caused a violent brawl between MPs that put one in hospital.