The Pentagon said Friday that 34 U.S. 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 spokesman.

President Donald Trump had initially said he was told that no troops had been injured in the Jan. 8 strike. The military said symptoms were not immediately reported after the strike and in some cases became known days later.

Defense Secretary Mark Esper arrives to brief members of the Senate on the details of the threat that prompted the U.S. to kill Iranian Gen. Qassem Soleimani in Iraq, Wednesday, Jan. 8, 2020 on Capitol Hill in Washington. (AP Photo Jacquelyn Martin)

Defense Secretary Mark Esper arrives to brief members of the Senate on the details of the threat that prompted the U.S. to kill Iranian Gen. Qassem Soleimani in Iraq, Wednesday, Jan. 8, 2020 on Capitol Hill in Washington. (AP Photo Jacquelyn Martin)

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.