Police in northwestern Pakistan said Friday a suicide bomber detonated himself during afternoon prayers at the Darul Uloom Haqqania seminary, killing at least six worshipers and wounding more than a dozen others.

Haqqania, with several thousand students, is located in the Khyber Pakhtunkhwa province and is among South Asia's largest and most respected Islamic seminaries. The top leaders of Afghanistan’s Taliban also studied at the madrasa in the town of Akora Khattak.

Seminary head Maulana Hamidul Haq was among those killed, and the death toll was expected to rise, according to local hospital officials.

The provincial police chief, Zulfiqar Hameed, confirmed the casualties, saying an investigation into the bombing was underway.

Pakistani Prime Minister Shehbaz Sharif condemned what he called "a cowardly and heinous act of terrorism,” according to a statement issued by his office.

No group immediately claimed responsibility for the blast, but suspicions fell on a regional Islamic State group affiliate, the Islamic State-Khorasan, or IS-K.

The group, which the United Nations says is based in neighboring Afghanistan, has taken credit for other madrasa attacks in Khyber Pakhtunkhwa.

IS-K has routinely carried out high-profile attacks against leaders and clerics affiliated with the Taliban government in Kabul, killing dozens of them in recent months.

A U.N. Security Council assessment this month described IS-K as “the greatest extra-regional terrorist threat.”

The report said that in addition to attacks on Taliban authorities and Afghan religious minorities, IS-K supporters conducted strikes as far away as Europe, and it “was actively seeking to recruit from among Central Asian states” bordering Afghanistan.