Police in Pakistan say gunmen have shot and killed a senior officer who was investigating sectarian killings in the country's southwest.

Officials say the assailants opened fire on Jamil Kakar's car Friday in Quetta, the capital of Baluchistan province, and fled the scene.

No one claimed responsibility for the attack. Authorities say Kakar was probing sectarian killings in Quetta.

Earlier this week, New York-based Human Rights Watch accused the Pakistani government of failing to apprehend attackers or prosecute extremist groups carrying out attacks against minority Shi'ite Muslims.

The New York-based rights group says 320 Shi'ites have been killed in targeted attacks this year, many in Baluchistan.

In one of the deadliest attacks, gunmen last month killed 22 Shi'ites after ordering them off buses in the southwestern province of Baluchistan. Just last week, eight Shi'ite members of the ethnic Hazara community were killed in two attacks in Quetta.