Awat Jeza, an intelligence officer wearing a surgical mask and gloves, stood before 130 of the kneeling men, who had all arrived on Sunday at the Asayish headquarters in Dibis, outside Kirkuk. He pulled down his mask as he told any fighters to step forward.

“Tell us who is ISIS,” he said. “If you were ISIS even one minute, one hour, one day, get up now.

“Later we have lists of names and we will find out. If you are honest, you may go free. If one of you surrenders now and tells us the truth, we will be merciful with you, but if you don’t, we will be —” Mr. Jeza paused, perhaps to choose the right word — “difficult.”

Just in the Dibis headquarters on Sunday, there were at least 300 fighting aged men, and similar numbers arrived on both Saturday and Friday.

Of the Sunday arrivals, about 60 were singled out and tied up as Islamic State suspects — plastic cuffs were brought in later to replace the scarves — and separated from the others. They were taken to smaller rooms, and in addition to bowing and kneeling, they were arranged so that all they could see was the wall in front of them.