Tens of thousands of people have protested in the Ukrainian capital, Kiev, against plans to sharply raise gas and electricity prices.
Many protesters came from the industrial east of Ukraine
A BBC correspondent in Kiev said the protests were as big as those during the 2004 Orange Revolution, which swept President Viktor Yushchenko to power.
Consumers face a near doubling of gas and electricity prices from 1 July, Ukraine's trade unions say.
Russia doubled the price of gas supplies to Ukraine earlier this year.
Left-wing opposition groups joined trade unionists at the Kiev demonstration.
Yulia Tymoshenko, set to return as Ukraine's prime minister this week, has called for the controversial gas supply deal with Russia to be reviewed.
Ukraine agreed to almost double what it pays for its neighbour's gas after a bitter price dispute which saw Russia cut off supplies for three days in January.
Ukraine, which imports most of its gas from Russia, is now paying $95 (£52) per 1,000 cubic metres for its gas - compared to $50 (£27) this time last year.
January's dispute between the two countries disrupted gas supplies to western Europe, prompting the European Union to review its approach to energy security.