Story highlights One bus is destroyed and two others are damaged, an official says

All three buses were carrying Shiite pilgrims headed toward Iran

It was not immediately clear who carried out the attack

A blast killed 20 Shiite pilgrims and injured another 25 in Pakistan's troubled southwestern Balochistan province Sunday, a senior administration official said.

Militants targeted three buses of Shiite pilgrims in the Dringarh area with a car bomb, said Tufail Baloch, deputy commissioner of the Mastung district.

One bus was destroyed in the attack, and the other two were damaged, Baloch said.

He said buses were carrying Shiite pilgrims from Quetta to Iran. The pilgrims were from Pakistan's Punjab and Khyber-Pakhtunkhwa provinces.

Baloch said authorities found a timed device at the scene that indicates the blast was controlled remotely.

It was not immediately clear who carried out the attack. But in the past, Sunni militant group Lashkar e Jhangvi has targeted buses of Shiite pilgrims.

Shia Islam is a minority sect in the mainly Sunni Muslim country, and its members face persecution from extremists.