Police fired teargas and used batons to disperse hundreds of protesters in Kiev today after parliament voted to make Russian, rather than Ukrainian, the main language in schools and local government in some parts of the former Soviet republic.
The clashes occurred after protesters, led by opposition members of parliament defending the role of Ukrainian as the only state language, massed in front of a building where President Viktor Yanukovich was due to hold a press briefing.
The chamber rushed the language bill through yesterday, minutes after a surprise proposal by a pro-Yanukovich deputy, giving opponents little time to cast their vote and prompting scuffles both in parliament and on the streets.
Though the bill needs Yanukovich's signature and that of parliament speaker Volodymyr Lytvyn - who has offered to quit - to become law, protesters took to the streets and stayed there overnight to bring pressure to bear on the president.
"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 took part in today's protest.
The two-metre (6ft 7 inches) Klitschko himself had to have his eyes washed out after being sprayed with teargas. His left arm was bandaged because of a cut sustained in the commotion.
Protesters urged Yanukovich, who had planned a celebratory statement to crown the successful co-hosting of the Euro 2012 soccer tournament, to veto the bill, which was pushed through by his own majority Party of Regions.
Opposition parties and millions who speak Ukrainian as their first language see the bill as a threat to sovereignty, keeping Ukraine in Russia's sphere of influence after 20 years of independence following the break-up of the Soviet Union.
As black-helmeted riot police moved to push the crowds back, Lytvyn himself tendered his resignation, apparently siding with the opposition which complained of procedural irregularities.
Yanukovich cancelled his briefing and called an urgent meeting with faction leaders and Lytvyn.
He said Ukraine may have to hold an early parliamentary election if the crisis persisted.. But since an election is already set for Oct. 28, this seemed more of a rhetorical flourish by Yanukovich aimed at preventing the situation from undermining his own prestige.
People in large swathes of Ukraine speak Russian as their mother tongue and the bill would recognise it as a regional language in predominantly Russian-speaking areas in the heavily industrialised east and southern regions such as Crimea.
The bill will be welcomed particularly in neighbouring Russia whose leaders have pressed Yanukovich to deliver on an election pledge in 2009 to upgrade the status of Russian.
Russian President Vladimir Putin is due to visit Ukraine on 12 July for a meeting with Yanukovich in Yalta on gas supplies when the language law seems certain to crop up in conversation.
But given the level of protest, it is by no means certain that Yanukovich will sign the bill into law even though it will be popular in his power base in the east of the country.
Opponents of the bill say it was pushed through by Yanukovich's party in order to win back disenchanted voters in Russian-speaking regions ahead of the October poll.
"This bill would push the Ukrainian language out of use," said one of the protesters, 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, opposition party Batkivshchyna said.
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 its activists blocked the entrance into the regional government building, Batkivshchyna said.