The Pentagon has said 34 US troops were diagnosed with traumatic brain injuries suffered in this month’s Iranian missile strike on an Iraqi air base.
Half of the troops have returned to their military duties, it added.
Seventeen of the 34 are still under medical observation, said Jonathan Hoffman, the chief Pentagon spokesman.
President Donald Trump had initially said he was told that no troops had been injured in the January 8 strike.
The military said symptoms were not immediately reported after the strike and in some cases became known days later.
After the first reports that some soldiers had been hurt, Mr Trump referred to them as “headaches” and said the cases were not as serious as injuries involving the loss of limbs.
Mr Hoffman’s disclosure that 34 had been diagnosed with traumatic brain injury (TBI) was the first update on the number injured in Iran’s missile attack on Ain al-Asad air base in western Iraq since the Pentagon said on January 17 that 11 service members had been flown out of Iraq with concussion-like symptoms.
Mr Hoffman said that of the 34 with TBI, 18 were evacuated from Iraq to US medical facilities in Germany and Kuwait, and 16 stayed in Iraq.
Seventeen of the 18 evacuees were sent to Germany, and nine remain there; the other eight have been transported to the United States for continued observation or treatment.
The one American sent to Kuwait has since returned to duty.
All 16 of those who were diagnosed with TBI and remained in Iraq have since returned to duty, Mr Hoffman said.
No-one was killed in the attack on Ain al-Asad.
The strike was launched in retaliation for a US drone missile strike that killed General Qassem Soleimani, the most powerful military general in Iran, on January 3 at Baghdad International Airport.