Clashes have broken out in front of Ukraine's parliament between unruly demonstrators and lines of police guarding the building.

Passions ran high outside the building Tuesday as deputies repeatedly voted down proposals to officially recognize a contentious World War II-era Ukrainian partisan group as national heroes.

Thousands of Svoboda nationalist party supporters rallied earlier in the day in celebration of the Ukrainian Insurgent Army, whose struggle for national independence was tainted by its collaboration with the Nazis.

Later, masked men attacked and threw firecrackers at police outside parliament as a session was taking place inside.

Svoboda denied its members were responsible for the unrest outside parliament and urged police to adopt any necessary measures to prevent casualties.