QUETTA, Pakistan —  Police raided several homes in southwestern Pakistan, arresting 15 suspected Islamic militants and seizing hand grenades that were likely to be used against Shiite Muslims during the religious festival of Ashoura (search), police said Saturday.

Friday's arrests came hours after two alleged members of an outlawed Sunni militant group blew themselves up with bombs when police raided a house in Quetta (search) on a tip that some suspects were hiding there. The pair belonged to Lashkar-e-Jhangvi, which is accused of killing hundreds of Shiites in recent years, police say.

City police chief Rafi Pervez Bhatti said they are holding 15 suspects from the outlawed group. "These people wanted to attack Shiites' processions during Ashoura on Sunday," he said, but gave no other details.

During the festival, Shiites (search) mourn the 7th century death of Imam Hussein, a grandson of the prophet Muhammad who was killed in a battle for leadership of the faith. His death deepened a rift between Shiite and Sunni Muslims that is still in evidence today.

In recent years, Ashoura has been marred by killings. Last year, Sunni suicide attackers hit a Shiite procession in Quetta, leaving 46 people dead.

This year, authorities deployed thousands of troops, police and paramilitary forces throughout Pakistan to prevent any religiously motivated clashes.

Although most of Pakistan's Sunni and Shiite Muslims live peacefully together, small radical groups on both sides often attach each other's leaders.