Tens of thousands marched through Warsaw Tuesday afternoon to celebrate the anniversary of Polish independence, and for the fourth consecutive year the procession erupted in violence. Riot police in the Polish capital used water cannon and fired rubber bullets into the air when several hundred masked men broke away from the march and attacked them with stones and flares, following peaceful celebrations earlier in the day led by President Bronisław Komorowski, according to several news reports.

Warsaw police spokesman Mariusz Sokolowski said more than 200 people had been detained Tuesday — many of them before the march began for carrying items that could be used as weapons. Sokolowski also said 32 people were injured in the violent clash, 12 of them police officers, Police Radio reported.

Nationalist groups who believe traditional Polish values — including a strong attachment to the Catholic Church and opposition to abortion and same-sex marriages — are under threat have made this march each year in Warsaw, to mark the day Poland regained its independence at the end of World War I in 1918, according to Reuters. The march organizers blamed outsiders for the violence. “As every year, people caused trouble at the front of the march,” the National Movement’s Krzysztof Bosak told Polish Radio’s IAR news agency, adding that the masked men were not part of the demonstration.

Violent clashes have marred Poland’s Independence Day celebrations for four years in a row. Last year, 12 police officers were injured and more than 70 people arrested when masked youths launched an attack on the Russian Embassy and set fire to a 82-foot wide “rainbow” archway that was a symbol of gay rights and tolerance.