A power struggle inside the government in Ukraine has brought tens of thousands of demonstrators out on to the streets of the capital, Kiev.
Amid a sea of flags, rival supporters - some supporting the president, others the PM - gathered in the city centre, defying a court order banning protests.
Pro-Western President Viktor Yushchenko has threatened to dissolve parliament and call new elections.
The pro-Russian governing coalition led by Viktor Yanukovych resists the move.
More than 10,000 people attended the rally in support of Mr Yanukovych, who says the president should back down.
Just a short distance away tens of thousands of orange flags of presidential supporters were being brandished, just where the Orange Revolution took place in late 2004.
Today's situation... cannot be resolved without revolution; today's government is not the voice of the people
A Yushchenko supporter
They are demanding an early election, claiming that power is being usurped from the president illegally by the ruling coalition.
Police in bulletproof vests patrolled the barriers set up to separate the rival protesters, and asked people moving from one square to another to put away political flags and scarves.
This political crisis is one of the most serious ever faced in Ukraine, with both sides determined to get their way even if it means more protests, says the BBC's Helen Fawkes in Kiev.
"It is not the best way to make revolution, twice, but today's situation... cannot be resolved without revolution; today's government is not the voice of the people, it only wants to make some profit," one Yushchenko supporter told the BBC.
The rival rallies went ahead even though a court had banned protests in the capital.
Bitter rivals
Mr Yushchenko defeated Mr Yanukovych in the presidential election of January 2005, following the pro-democracy Orange Revolution.
Ukrainian President Viktor Yushchenko
Mr Yushchenko accuses his rival of seeking to usurp power
But he was forced to accept him as the head of government after his allies failed to win a majority in the March 2006 parliamentary election.
Mr Yushchenko has expressed concern that Mr Yanukovych could strengthen his parliamentary majority, enabling him to override presidential vetoes and amend the constitution.
On Saturday, he accused Mr Yanukovych of seeking to usurp power by trying to win pro-Western MPs over to his coalition and opposing his pro-Western policies.
"I want to say that unless the majority resumes its work on the basis of the constitution, I will sign a decree disbanding parliament," he told a meeting of his political party to loud applause.
He further accused the coalition of lacking the "political will and desire to support stability".