A faction of Pakistani Sunni militant group Lashkar-e-Jhangvi (LeJ) cooperated with Islamic State this week in an attack on a police college that killed 59 people, the group's spokesman told Reuters on Wednesday.
The confirmation of a link between the two Sunni extremist groups will stoke fears that Middle East-based Islamic State is building a presence in Pakistan by aligning with domestic militant outfits.
Islamic State claimed responsibility for Monday's attack in Pakistan's southwestern city of Quetta and released photographs of the purported gunmen, who hunted down and killed police cadets during a raid that lasted nearly five hours.
But Pakistani authorities, who in September said they had crushed Islamic State's efforts to enter Pakistan, pinned the blame for the assault on an LeJ faction, Al Alami.
"We have no direct link with Daesh, but we have done this attack together," said Ali bin Sufyan, spokesman for LeJ Al-Alami, using an Arabic acronym for Islamic State.
Sufyan declined to elaborate on the help Al Alami provided to Islamic State in Quetta, the provincial capital of Pakistan's vast but impoverished Baluchistan region.
"We will provide help to anyone who asks against Pakistani security forces, and we will also accept help for this," Sufyan added.
LeJ, whose roots are in the heartland Punjab province, has a history of launching sectarian attacks in Baluchistan, particularly against the minority Hazara Shias. Pakistan has previously accused LeJ of colluding with al Qaeda.
Authorities launched a crackdown against LeJ last year, particularly in Punjab. In a blow to the group, Malik Ishaq, its leader, was killed in July 2015, along with 13 members of the central leadership in what police call a failed escape attempt.