Tens of thousands of people have marched through the centre of Ukraine's capital, Kiev, demanding the resignation of the country's President, Leonid Kuchma.
The opposition vowed to continue its protests
Participants in the rally, organised by opposition parties, accused President Kuchma of corruption, illegal arms dealing with Iraq, abuse of office and vote rigging.
The demonstrators also blamed the president of being involved in the murder three years ago of a journalist, Georgiy Gongadze, and harassing the opposition media.
President Kuchma - who is currently on a visit to Slovakia - denies all the allegations, and accuses the opposition of trying to stall his reforms.
Today we gathered because Ukraine is in danger. The authorities are corrupt. They are killing freedom and democracy in Ukraine
Viktor Yushchenko, Our Ukraine party leader
The rally was taking place on the second anniversary of violent demonstrations against the government, in which dozens of protesters and also the police were injured and hundreds arrested.
Organisers of the so-called Rise Ukraine! rally claimed that as many as 50,000 people took to the streets of Kiev, although police said up to 30,000 attended.
Many participants said Kuchma had made them poor
The demonstrators - many carrying national flags and anti-presidential banners - chanted "Down with Kuchma" and "No to dictatorship".
The rally was organised by former Prime Minister Viktor Yushchenko's Our Ukraine party and Yulia Tymoshenko's centre-right block.
"Today we gathered because Ukraine is in danger. The authorities are corrupt. They are killing freedom and democracy in Ukraine," Mr Yuchshenko said.
The supporters of the Communist Party and the Socialists also joined the rally, accusing Mr Kuchma of damaging Ukraine's economy and impoverishing the people.
"He [Kuchma] has made us poor, that's why we are protesting," Halyna Pugachova, aged 66, was quoted as saying by the Associated Press news agency.
"Our pensions haven't been paid. All our savings disappeared. That is why everybody is unsatisfied with Kuchma - students, pensioners, everybody."
The anti-Kuchma protests - which the opposition said took place in dozens of cities across Ukraine - were the first opposition-led action this year.
But Ms Tymoshenko said the protests would continue until President Kuchma stepped down or called early elections.
Weathering the storm
The protests came only days after President Kuchma unveiled proposals to give more of his powers to parliament.
President Kuchma says he will fight any attempts to stall his reforms
Mr Kuchma said the constitutional reform was aimed at resolving destructive confrontation between the executive and legislative branches.
He urged Ukrainians to back his proposals during a popular debate and accused the opposition of stalling his reform drive.
"I am not going to put at risk the future of political reform and the future of the country. Let people discuss the main issues of the reform... and parliament should approve it," he said.
Mr Kuchma first suggested the transfer of some of his powers in August last year, just days before the nationwide opposition protests that nearly toppled him.
Some experts said the timing of the new initiative was an attempt by the president to strike a pre-emptive blow against the latest opposition protests.
Some analysts say his new proposals are a test to see if he can get enough support in parliament to change the constitution and stand for a third term.
Mr Kuchma was re-elected in November 1999 to a second five-year term, but has subsequently seen his poll ratings plunge.