Police in Hungary have fired tear gas on crowds of about 1,000 demonstrators during the 50th anniversary of the country's revolt against Soviet rule.
The local MTI news agency said tear gas was used outside parliament, where local and foreign officials had laid flowers to commemorate the revolt.
Prime Minister Ferenc Gyurcsany has faced bitter opposition after admitting that he lied to win re-election.
Some veterans of the 1956 uprising refused to shake hands with him.
MTI reported that tear gas was also used at Budapest's Western Railway Station and that water cannon was used at another location.
The agency said that the protesters had been throwing stones and pieces of metal at security forces.
A Reuters cameraman said 20 tear-gas canisters had been fired, along with rubber bullets.
Police had earlier broken up angry protests ahead of formal ceremonies to mark the 1956 uprising and cleared hundreds of protesters from Hero's Square in the city centre.
Protesters have been present outside parliament for weeks.
President Laszlo Solyom has appealed for national unity.
He said the entire nation shared the demand for Hungarian independence during the uprising, which was suppressed in a bloody intervention by Soviet forces.
Monday's events began with dignitaries taking turns to place white roses at the black marble monument to the uprising outside parliament, before heading inside to adopt a declaration of freedom.
There was also to be a ceremony of remembrance at the statue of Imre Nagy, who was the reformist prime minister at the time.
But parallel to all the official events are those held by opposition groups, says the BBC's Nick Thorpe in Budapest.
Several groups are marching through the city to events at different locations. It is a confusing picture, and difficult to tell whether the groups carrying Hungarian flags are marking 1956 or taking part in anti-government protests, our correspondent says.
The main opposition Fidesz party said it was boycotting official anniversary events at which Prime Minister Gyurcsany is speaking, and holding its own rally close to the state radio building, the scene of bitter fighting in 1956.
Mr Gyurcsany caused political uproar recently when he admitted he had lied to the public about the economy.
But he denied any comparison between Monday's protests and their 1956 counterparts.
"Despite the often justified disappointment and discontent, the majority of Hungarians believe that parliamentary democracy is the most suited to express people's will and to create law and give a programme to a free Hungary," he said.
The protest was crushed less than two weeks after it began
The uprising started in Budapest on 23 October 1956, with a spontaneous demonstration by a crowd of about 23,000, the reading of a pro-democracy manifesto and the singing of banned national songs.
A giant statue of Stalin was pulled down, leaving only the dictator's boots on the pedestal.
Soviet tanks were forced to withdraw, but returned with devastating force a week later.
Imre Nagy, the reforming prime minister, made a final impassioned plea to the outside world by radio.
He and hundreds of others were arrested and executed, among thousands of Hungarians who died.
The BBC's Allan Little says the uprising was the moment the world accepted the post-war partition of Europe and the apparent permanence of what Winston Churchill had called "the Iron Curtain".