WASHINGTON — The Defense Department said on Thursday that 64 troops had sustained traumatic brain injuries after the Iranian ballistic missile strikes on Ayn Al Asad Air Base in Iraq this month, up 14 from an earlier announcement this week.

The number, which has steadily increased since the Jan. 8 attack, is a clear indicator of the lasting and unseen effects so common in America’s long wars, made strikingly prevalent by the roadside bombs scattered in Iraq and Afghanistan that killed and maimed thousands of troops.

Eight are being treated in the United States, while 21 are in Landstuhl, Germany, and 39 have returned to duty in Iraq, according to a Pentagon statement. The higher number of 64 was first reported by CNN.

Defense Secretary Mark T. Esper, speaking to reporters during a news conference alongside the chairman of the Joint Chiefs of Staff, Gen. Mark A. Milley, said on Thursday that the Pentagon took those types of injuries “very seriously.”