Later, the governor gave the Mahdi Army 24 hours to back down.
The Mahdi Army is believed to have around 60,000 members.
"We don't have any of these things in the Mahdi Army."
When the Mahdi Army took control of the city last month, the local government and police force collapsed.
The Mahdi Army is believed to be responsible for the attack.
Most of the police fled the day the Mahdi Army rose.
"You have to ask the people here what the Mahdi Army did for this mosque," he said.
"They're really very dangerous people," he said of the Mahdi Army.
But the agreement did not include the Mahdi Army, which has thousands of fighters.
At least eight of those killed were from the Mahdi Army, the sheik said.