President Barack Obama has said he will send about 200 more US troops to Iraq to protect Americans and the US embassy in Baghdad amid fierce fighting in the country between government forces and Sunni armed groups.
The US is also sending a detachment of helicopters and drone aircraft.
Pentagon spokesman Rear Admiral John Kirby said on Monday about 200 forces arrived in Iraq on Sunday to reinforce security at the US embassy, its support facilities and the Baghdad International Airport.
Another 100 personnel were also due to move to Baghdad to "provide security and logistics support."
"These forces are separate and apart from the up to 300 personnel the president authorised to establish two joint operations centres and conduct an assessment of how the US can provide additional support to Iraq's security forces," Kirby said in a statement.
Of the initial deployment to the embassy of 275 troops earlier this month, 100 had been on standby outside the country, but are now moving into positions in Baghdad, the Pentagon said.
The announcement will bring to nearly 800 the total number of US forces in and around Iraq to train local forces, secure the embassy and protect Washington's interests.
President Obama has ruled out sending combat troops back into Iraq. But he says the additional troops will be equipped for combat.
Obama says the troops will stay in Iraq until security improves so that the reinforcements are no longer needed.