Pakistan blast

Pakistani Shiite Muslims search the wreckage of a destroyed bus after a bomb attack about 30 miles southwest of the provincial capital of Quetta. (Banaras Khan / AFP/Getty Images / January 21, 2014)

PESHAWAR, Pakistan – An explosion tore through a bus carrying Shiite Muslim pilgrims in western Pakistan on Tuesday, killing at least 22 people and injuring dozens.

Pakistani media reports said the bus was traveling from the Iranian border through volatile Balochistan province when it was struck about 30 miles southwest of the provincial capital, Quetta.

Shafqat Anwar, the assistant commissioner in Mastung district, told reporters that at least 32 people were injured.

Two vehicles carrying security forces who were escorting the pilgrims’ buses were also damaged in the blast, officials said.

No group immediately claimed responsibility for the attack, but Sunni Muslim militant groups operating in the area have routinely targeted Shiites, who make up about 20% of Pakistan’s population.

Three weeks ago, a car bomb ripped through a bus carrying Shiite pilgrims near Quetta, killing one person and injuring 24 others. Jaish al Islam, a banned militant group, claimed responsibility for that attack.

Ethnic nationalist groups in Balochistan also have been waging a long-running insurgency demanding greater autonomy from the central government in Islamabad.

Investigators said that about 170 pounds of explosives were used in Tuesday’s attack, according to media reports, but it was unclear whether it was a suicide bomb or if the explosives had been planted.

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Ali is a Times special correspondent.