The US is to send 200 extra troops to Iraq to help fight so-called Islamic State (IS), officials say.
The deployment will increase the number of US personnel in Iraq to about 4,100.
Alongside the additional troops, Apache attack helicopters will be deployed for the first time against IS in Iraq.
US Defence Secretary Ash Carter made the announcement during an unannounced visit to Baghdad, where he met with US military officials and Iraqi Prime Minister Haider al-Abadi.
The US also plans to give Kurdish Peshmerga forces, which are fighting IS on the ground, more than $400m (£280m; €350m) in assistance.
Co-operation between the two forces was evident on Monday when Kurdish officials said they had killed a senior IS commander in the south of Mosul in a joint raid with US special forces.
According to the officials, the operation in Hamam Alil resulted in the death of Salman Abu Shabib al-Jebouri, a leading member of the IS military council, and two of his aides.
Most of the additional 200 US troops will be special forces, according to the Associated Press. The remainder will include trainers, security forces for the advisers, and maintenance crews for the Apaches.
The Apaches would help Iraqi forces to recapture the country's second city of Mosul from IS, Mr Carter said.
The US is leading an international coalition that has been bombing IS targets since August 2014.
IS seized large areas of Iraq, north and west of Baghdad, in 2014, but Iraqi forces have recaptured significant ground from the jihadists in recent months.
Analysis: Gary O'Donoghue, Washington Correspondent
The Pentagon has been arguing for some time that it should increase the numbers of troops and in particular special forces in Iraq. It now seems that Defence Secretary Ash Carter has got the White House to agree.
The enlarged presence is likely to see the numbers of US troops close to the front line rise, as the advise and assist role they undertake means they work closely with their Iraqi counterparts involved in the fighting.
Just last month, a US marine was killed in combat when the Islamic State Group fired Katyusha rockets at a base close to Mosul. This stepping up comes as the battle for Mosul starts to become a reality. Iraq's second largest city is seen as key in the war to squeeze IS out of Iraq and Syria.