Police fire teargas at angry crowds and parliament speaker offers to step down as bill is passed

Police have fired teargas and used batons to disperse hundreds of protesters in Kiev and Ukraine's parliament speaker has offered to quit after the passing of a law to boost the status of the Russian language in the former Soviet republic.

Protesters, led by opposition members of parliament defending the role of Ukrainian as the only state language, massed in front of a building where the president, Viktor Yanukovich, was due to hold a press briefing.

The chamber approved the language bill on Tuesday, minutes after a surprise proposal by a pro-Yanukovich deputy, giving opponents little time to cast their vote, prompting brawls in parliament and on the streets.

"There are millions of us and they cannot pretend that nothing has happened," said Vitali Klitschko, the world heavyweight boxing champion who has founded his own opposition party – Udar (Blow) – and who was among protesters.

Protesters urged Yanukovich, who had planned a celebratory statement after the successful co-hosting of the Euro 2012 soccer tournament, to veto the bill, pushed through by his own majority Party of Regions.

Yanukovich cancelled the briefing and called an urgent meeting with leaders of major factions and the parliament's speaker, Volodymyr Lytvyn, who had asked for amendments to the bill and tendered his resignation because of the way it was forced into law.

The president later said Ukraine might have to hold an early parliamentary election if the crisis in the chamber persisted.

The parliament's website said Mykola Tomenko, a deputy speaker, had also stepped down. Tomenko is a member of the jailed opposition leader Yulia Tymoshenko's BYuT parliamentary faction.

The bill, which will not become law until first Lytvyn and then Yanukovich have signed it, would recognise Russian as a "regional" language in predominantly Russian-speaking ares, enabling its use in the public service.

Opponents of the bill say it was pushed through by Yanukovich's party in order to win back disenchanted voters in its Russian-speaking power base before a parliamentary election in October.

But opposition parties and millions who speak Ukrainian as their first language see the bill as a potential threat to Ukrainian sovereignty.

"This bill would push the Ukrainian language out of use," said one of the protesters, the 40-year-old entrepreneur Yuri Chernyak. "It might be too late but we must do something and not stay indifferent."

More protests were planned across the country, the opposition party Batkivshchyna said, and many protesters stayed out on the streets of central Kiev overnight.

Another opposition leader present at the scene of the Kiev protests, Arseniy Yatsenyuk, said: "There are all signs of a real political crisis in Ukraine and it will develop further."

A protest also took place in the western city of Lviv, where activists blocked the entrance to the regional government building, Batkivshchyna said.

People in large swathes of Ukraine, notably the eastern industrial heartland, speak Russian as their first language.

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