[Update: The Pentagon now says 50 troops sustained brain injuries in the strike.]

WASHINGTON — The Defense Department said Friday that 34 American service members have traumatic brain injuries from Iranian airstrikes on Al Asad Air Base in Iraq, contradicting President Trump’s dismissal of injuries among American troops this week.

A Pentagon spokesman, Jonathan Hoffman, told a news conference that eight of the affected service members have returned to the United States from an American military hospital in Germany.

On Wednesday, Mr. Trump dismissed concussion symptoms felt by the troops as “not very serious,” even as the Pentagon acknowledged that a number of American service members were being studied for possible traumatic brain injury caused by the attack.

“I heard they had headaches,” Mr. Trump said at a news conference in Davos, Switzerland. “I don’t consider them very serious injuries relative to other injuries I have seen.”