QUETTA, Pakistan: At least 22 Shiite pilgrims returning from Iran were killed and 20 others wounded when a bomb hit a bus in the southwest Pakistan province of Baluchistan Tuesday, officials said.

The attack took place at Dringhar village on the Pakistan-Iran highway some 60 kilometers (37 miles) west of Quetta, Baluchistan’s capital.

“At least 22 people were killed and 20 others were wounded,” local government official Shafqat Shahwani told AFP.

He said 51 passengers had been on board at the time of the blast and that nine passengers were still unaccounted for due to the extent of carnage caused.

Provincial home secretary Asad Gilani said it was not immediately clear what type of bomb was used or whether it was a suicide attack.

He said that two buses had been traveling together with security vehicles provided by the government and that the bomb struck one of the buses.

Two people were killed in a similar attack on January 1 when a bomb targeted a bus carrying Shiite pilgrims.

Nobody claimed responsibility for that attack but there has been a rise in sectarian violence in Pakistan after several deadly clashes between Sunni and Shiite Muslim groups near Islamabad in November last year.

Shiites make up around 20 percent of Pakistan’s population, which is largely Sunni Muslim.

Oil and gas-rich Baluchistan has been badly hit by a decade-long Baluch separatist insurgency and sectarian violence, mainly targeting Shiite Muslims from the Hazara ethnic community.