The violence broke out during a peaceful protest in front of parliament of more than 2,000 people, including students, farmers and green activists, who said they were fed up with life in the European Union's poorest and most corrupt nation.

Protesters demanded the Socialist-led government step down for its failure to tackle widespread graft and crime and solve economic problems in the face of a global slowdown. Some shouted "Resign" and "Mafia".

Dozens of demonstrators hurled snowballs and bottles at parliament and clashed with police about an hour after the rally started. Some of the protesters were injured.

Police said they had arrested several people carrying hand-made grenades, without giving further details.

Riots also broke out in economically troubled Latvia on Tuesday evening after an earlier peaceful anti-government demonstration.

"We are fed up with living in the poorest and most corrupt country," organisers of the Sofia protest said in a statement. "This a unique protest which unites the people in their wish for a change and their wish to live in a normal European country."

Opinion polls show over 70 percent of the 7.6 million population want the government to quit and 75 percent disapprove of parliament's work, citing a lack of progress in the anti-corruption fight.

The EU last year punished Bulgaria for being too slow in cracking down on graft and organised crime by suspending hundreds of thousands of euros in EU aid.

Last year's report by Transparency International portrayed the Balkan country as the most corrupt EU nation, taking the lead from neighbouring Romania.

Protests are expected to accelerate ahead of this summer's general elections but are unlikely to topple the government, which has an overwhelming majority in parliament, observers say.