ISLAMABAD, Pakistan (AP) _ A coal mine explosion in southwestern Pakistan killed seven workers and injured another 13, the state-run news agency said on Thursday.

The explosion late Wednesday in southwestern Baluchistan was caused by a build up of methane gas, according to The Associated Press of Pakistan, which quoted Ghulam Sarwar Lodhi, Pakistan's chief inspector of mines.

A three-hour rescue operation freed 13 workers, who were taken to hospital.

The mine was closed and Lodhi ordered an investigation into the accident.