LAHORE, Pakistan - Pakistani police killed the leader of the sectarian militant group Lashkar-e-Jhangvi, his two sons and 11 others on Wednesday in a shootout after gunmen attacked a police convoy and freed him as he was being moved, police said.

Malik Ishaq was on a US list of terrorists and the group he founded has claimed responsibility for the deaths of hundreds of civilians, mostly minority Shi'ite Muslims.

He has faced several murder trials but always been acquitted after witnesses refused to testify. He was arrested again on Saturday, under a public order act, along with his two sons.

On Tuesday, police took Ishaq and the sons to an area near the Punjab province town of Muzaffargarh where they had seized an arms cache, to identify men they had detained on suspicion of being members of Ishaq's group.

As the police convoy returned in the early hours of Wednesday, a group of men on motorcycles ambushed them, freeing Ishaq and his two sons, police said.

"Twelve to 15 terrorists attacked the police party ... freed the accused and fled away on motorcycles," a police spokeswoman, Nabila Ghazanfar, quoted a policeman in the area as saying in a message.

Police further along the road attacked the gunmen as they were fleeing, killing Ishaq, his two sons, and 11 others, Ghazanfar cited the policemen as saying in her message.

Six police were wounded, he said.

"The accused, in custody, were under investigation for murder of dozens of people in target killings," the policeman said.

"The gang was also in league with the (Taliban) and al Qaeda groups operating in the area."

The circumstances of Ishaq's killing are bound to raise questions given a long police record of staging such encounters to eliminate suspects.

One senior police investigator not involved in this case, said police often staged such clashes as they did not have faith the courts would be brave enough to convict high-profile militants for fear of retaliation.

The investigator, who declined to be identified, said Ishaq's killing bore the hallmarks of police action under a National Action Plan (NAP) against militancy, launched last December after Pakistani Taliban militants killed 134 students at an army-run school in the city of Peshawar.

"This is NAP in action," the investigator said. "State policy on this is indiscriminate and broad-based: terrorists will not be tolerated, no matter who they are or what group they belong to."

Another senior police official said Punjab province was being put on alert in anticipation of retaliatory attacks.