Dozens of people were killed in northern Afghanistan on Sunday after an attack by Taliban fighters teamed up with a commander claiming allegiance to ISIS.

According to local officials, the Taliban joined forces with Sher Mohammed Ghazanfar, a local commander claiming allegiance to ISIS, to overrun the Mirza Olang area.

“According to our credible information, 50 people have been killed,” said Sharif Aminyar, the district governor of Sayad.

Aminyar noted that 18 of the people killed had been members of the afghan Local Police, a government militia, and other local militias supported by the government. The rest of the casualties were civilians.

“It was a joint Daesh (ISIS) and Taliban operation,” Aminyar said. “The Taliban were led by Mullah Nader and Daesh was led by Sher Mohammed Ghazanfar.”

Zabihullah Mujahid, a spokesman for the Taliban, denied cooperation with ISIS on the operation, saying local residents had misunderstood.

“Ghazanfar is not Daesh — he is our commander in Sar-e-Pul, a very active commander, and he is under our command, our flag.”

Many if ISIS’s attacks in Afghanistan have targeted the minority Shias, and often in brutal ways.

Last week, ISIS suicide bombers barged into a Shia mosque in the western city of Herat as worshipers were standing for evening prayer. The attack claimed the lives of at least 37 people.