Jozsef Bencze, head of the national police, said riot officers used tear gas and water cannon Monday evening to control more than 1,000 demonstrators in Budapest. Twenty protesters were arrested during the clashes, the Hungarian news agency MTI reported.

The anti-government, ultra-rightists tried to reach Budapest’s Opera House where Hungarian socialist Prime Minister Ferenc Gyurcsany attended ceremonies Monday marking the 51st anniversary of the Hungarian failed uprising against Soviet rule.

Three press photographers were injured as they took pictures of protesters throwing stones and flaming gasoline bombs at police blocking approaches to the Opera House.

Several vehicles, including a police water cannon, were burned in the rioting.