KARACHI — The Pakistani government announced a security operation against sectarian death squads in the western city of Quetta on Tuesday, four days after a sectarian bombing killed at least 89 people and led to unusually sharp criticism of the powerful military and its intelligence agencies.

Prime Minister Raja Pervaiz Ashraf vowed to target the extremists behind Saturday’s bombing, which killed dozens of women and children and targeted a neighborhood in Quetta where Hazara, minority Shi’ites, are concentrated.