Malik Ishaq, chief of banned sectarian outfit Lashkar-i-Jhangvi, his two sons Usman and Haq Nawaz, and 11 attackers were killed in an alleged exchange of fire with police personnel late on Tuesday night.

At least six policemen were injured in the alleged encounter.

Ishaq and his sons were arrested by the Counter-Terrorism Department a week ago. Following their recent arrest, the police had interrogated them and had subsequently taken them to Shahwala in Punjab's Muzaffargarh district to aid the police in recovering weapons and explosives, sources in the CTD said.

The encounter appears to have taken place as militants attacked security forces and tried to free Ishaq who was killed in the ensuing exchange of fire, security sources say.

A spokesman for CTD Multan said Ishaq, his two sons, one Ghulam Rasool Shah and two other accused, all from Lashkar-i-Jhangvi, were taken to Muzaffargarh by the counter-terrorism department to aid in the recovery of arms and explosives.