The US military in Iraq is facing growing political pressure over a raid on a Baghdad mosque complex that left about 20 people dead on Sunday evening.
Mourners have been burying bodies of the dead in Sadr City
US officials said 16 insurgents had been killed and 18 captured, along with a significant weapons cache.
However, members of Iraq's ruling Shia Islamist bloc say many of the dead were civilians taking part in prayers.
"Entering the mosque and the killings there are an unjustified and flagrant attack," the interior minister said.
"Approximately 18 innocent men who were inside the mosque performing sunset prayers were killed and became martyrs," Bayan Jabr added in an interview on Dubai-based al-Arabiya television. "They were killed unjustly and wrongfully."
Some members of the ruling Shia Islamist alliance repeated allegations - denied by US officials - that Americans and Iraqi troops under their command had tied people up at the Mustafa mosque in north-east Baghdad's Sadr City up and shot them in cold blood.
Earlier on Monday, a spokesperson for Prime Minister Ibrahim al-Jaafari said he was "deeply concerned" by the reports and had telephoned US military commander General George Casey, who had promised a full inquiry.
Baghdad Governor Hussein Tahan said all co-operation with US forces would be suspended unless the incident was investigated by a panel not including the US military.
The US military said the bloodshed happened after Iraqi commandos and soldiers from the Iraqi counter-terrorism force came under fire during a house-to-house search for insurgents.
It is in dispute whether the victims were armed insurgents
Members of the US special forces were present but only in an "advisory capacity", officials said.
The fighting took place in an office adjacent to the mosque, the US military said.
Large numbers of weapons were found, the US military said, and an abducted employee of the ministry of health was freed, after a 12-hour ordeal of beating.
Iraqi police said the dead included seven members of the Mehdi Army, the militia loyal to Shia cleric Moqtada Sadr, three members of another Shia Islamist party and seven civilians with no party affiliation.
News footage taken after the attack seemed to belie US assertions that troops had not entered or damaged any sacred building during the raid.
The room where the killing occurred appeared to be a prayer hall. The floors are carpeted and the walls covered with religious posters.
The tape showed a tangle of male bodies and spent 5.56mm bullet casings on the blood-smeared floor - the kind of ammunition used by the US military.
"In our observation of the place and the activities that were going on, it's difficult for us to consider this a place of prayer," said US military spokesman Barry Johnson.
"It was not identified by us as a mosque, though we certainly recognised it as a community gathering centre. I think this is frankly a matter of perception," he added.
The area is a stronghold of the Mehdi Army.