The police said Tuesday that they have opened a probe into possible law violations and violence during a rally the previous day by conservative activists in front of the National Assembly building.

Some 500 people belonging to right-wing organizations and supporting the main opposition Liberty Korea Party held a rally in protest against a set of reform bills.

Following the rally, the protesters remained there for nearly nine hours, tried to break into the National Assembly building and some of them swore at and spat at members of two minor left-leaning parties -- the Justice Party and Party for Democracy and Peace -- according to local reports.

The Yeongdeungpo Police Station said they were analyzing video footage to identify the leaders of what the police see as a potentially illegal rally. The rally had not been reported to the police in advance and rally participants refused to follow the police order to break up. They are also looking into whether there was any violence by the participants.

Some of the rally participants face charges of obstruction of justice and assault.

The Justice Party said it would file a complaint against unidentified rally participants and members of the Liberty Korea Party, including the party leader Hwang Kyo-ahn, for violence that erupted during the rally.

The rally came as the ruling Democratic Party and minor opposition parties are working to pass a set of reform bills -- ranging from election reform to the establishment of an independent body investigating corruption allegations involving high ranking officials. The main opposition party has fiercely protested the passage of the bills.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)