The Pentagon said on Friday that 34 US troops were diagnosed with traumatic brain injuries suffered in this month’s Iranian missile strike on an Iraqi air base, and that half of the troops have returned to their military duties.

Seventeen of the 34 are still under medical observation, according to Jonathan Hoffman, the chief Pentagon spokesperson. US 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, Trump referred to them as “headaches” and said the cases were not as serious as injuries involving the loss of limbs.

Hoffman said that of the 34 with TBI, 18 were evacuated from Iraq to US medical facilities in Germany and Kuwait, and 16 stayed back in Iraq. No one was killed in the attack on Ain al-Asad.