US troops have been called in to help Iraqi forces battle insurgents who attacked an army base in Baghdad, killing 12 people, officials say.
It marks the first such use of US troops since the end of US combat operations five days ago.
US forces remaining in Iraq can now only participate in operations at the request of Iraqi authorities.
A US military spokesman said US forces had provided fired as Iraqis located two of the assailants inside the base.
The BBC's Gabriel Gatehouse in Baghdad says reports from the scene are still confused, but piecing together events from different sources, the attack seems to have involved at least five bombers.
He says one of the bombers detonated his explosives at an outer checkpoint leading to the Rusafa military command headquarters, blowing up a mini-van.
Then, four men - some wearing suicide vests - ran towards the base. Two were reportedly shot dead before they could pass a second checkpoint.
An Iraqi officer at the scene told the BBC that two further bombers got into the base, taking refuge inside the building, and attacking security forces with hand grenades.
The same officer said that US forces were called in to help, and exchanged gunfire with the attackers before Iraqi security forces stormed the building, killing the bombers.
US military spokesman Lt Col Eric Bloom said the Iraqi military had also requested help from helicopters, drones and explosives experts.
More than 20 people were wounded in the incident.
The attack is the deadliest in Baghdad since the US formally ended combat operations last month.
The same compound was attacked by al-Qaeda in Iraq three weeks ago, when more than 50 recruits were killed.
