KABUL, Afghanistan (AP) — A powerful explosion in a mosque frequented by a religious minority group in northern Afghanistan on Friday has left several casualties, witnesses and the Taliban's spokesman said.

The blast occurred in a Shiite mosque in Kunduz province during the weekly Friday prayer service at the Gozar-e-Sayed Abad Mosque when members of the Shiite religious minority typically come in large numbers for worship. Witness Ali Reza said he was praying at the time of the explosion and reported seeing many casualties.

Taliban chief spokesman Zabihullah Mujahid said the Shiite mosque was the target and that a “large number” of worshippers were killed and wounded. He said Taliban special forces had arrived to the scene and were investigating the incident.

The cause of the blast was not immediately clear. No group has yet claimed responsibility for it.

The Taliban leadership has been grappling with a growing threat from the local Islamic State affiliate, known as the Islamic State in Khorasan. IS militants have ramped up attacks to target their rivals, including two deadly bombings in Kabul.

IS has also targeted Afghanistan’s religious minorities in attacks.