More than 2,000 religious students demanding the resignation of Prime Minister Benazir Bhutto attempted Monday to storm the Parliament building.
Riot police fired tear gas at the crowd and beat back protesters with sticks and clubs, preventing them from entering the building.
The students, supporters of the right-wing Party of Islam, pelted police with rocks and bricks.
Police arrested party chief Qasi Hussein Ahmed and other party leaders.
Sunday, police fired tear gas on thousands who tried to rush past barricades protecting the capital.
The Party of Islam accuses Ms. Bhutto's government of rampant corruption and mismanagement.