ISLAMABAD, Nov. 7 (Xinhua) -- A hand grenade attack on a patrolling team of security men injured 13 people in Pakistan's southwest on Saturday, police said.

    Hospital sources said four security men were among those injured in an attack at a crowded market in Quetta, the capital of Balochistan province, Deputy Superintendent Police, Ghulam Hussain Buzdar said.

    Buzdar said that unidentified men threw locally made bomb in Meezan Chowk locality, injuring passersby and vendors. He said the incident occurred when many people were busy shopping.

    Witnesses said that the bomb was thrown at the patrolling party of security men.

    The injured, including children, were shifted to Civil Hospital Quetta. Two injured are in critical condition, hospital sources said.

    No group claimed responsibility for the attack.

    Quetta has seen incidents of violence in recent days. Earlier, on the same day before noon, militants hurled a hand grenade into the premises of a girls school located near Mannu Jan Road in Quetta, injuring two students and two teachers.

    Meanwhile three policemen were injured in a roadside bomb attack near the city of Dera Ismail Khan in the country's northwest, police said.

Special Report: Pakistani Situation