3 killed in Pakistan mosque blast

ISLAMABAD, Pakistan (CNN) - An explosion inside a mosque in northwest Pakistan's tribal region on Saturday killed three people and injured four others, a government official said.

The explosion happened just after 4 p.m. (6 a.m. ET), leaving the Hangu district mosque in ruins inside Pakistan's North-West Frontier Province, said Omer Faraz Khan, deputy superintendent of Hangu.

He said rescuers were trying to save people trapped under the debris. It was not immediately clear how many people were inside the mosque at the time of the blast. Police are investigating the explosion.