The US is sending another 300 troops to Iraq to beef up security at the US Embassy and elsewhere in the Baghdad area to protect US citizens and property, officials said.
That raises the total US troop presence in Iraq to about 750, the Pentagon said.
The State Department announced that it was temporarily moving an unspecified "small number" of embassy staff in Baghdad to US consulates in the northern city of Irbil and the southern city of Basra. This is in addition to some embassy staff moved out of Baghdad earlier this month,
Department spokeswoman Jen Psaki said the Baghdad embassy "will be fully equipped to carry out" its mission.
The White House announced that president Barack Obama had directed that 200 troops be sent to reinforce security at the embassy, its support facilities and Baghdad International Airport.
The Pentagon said the 200 arrived over the past two days.
A spokesman said: "The presence of these additional forces will help enable the embassy to continue its critical diplomatic mission and work with Iraq on challenges they are facing as they confront Islamic State in Iraq and the Levant."
Mr Obama notified House and Senate leaders in a letter yesterday of the additional forces heading to Iraq. Officials said they will deliver a detachment of helicopters and drone aircraft to improve airfield and travel route security in Baghdad.
The president has ruled out sending combat troops back into Iraq. He said the extra forces will stay in Iraq until security improves so the reinforcements are no longer needed.
Another 100 troops who had been on standby in the Middle East since mid-June will also move into Baghdad to provide security and logistics support.
That raises to about 470 the number of US troops providing security in Baghdad.
Those forces are separate from the teams of up to 300 US military advisers Mr Obama authorised for deployment to Iraq last month. Of those 300, about 180 had arrived as of yesterday, the Pentagon said.
They are assessing the state of Iraqi security forces and co-ordinating with Iraqi authorities.
The US also has a permanent group of about 100 military personnel in the Office of Security Co-operation, at the US Embassy, to co-ordinate US military sales.