More than 100 American service members have traumatic brain injuries from Iranian airstrikes on Al Asad Air Base in Iraq in January, the Defense Department said, a number that was more than 50 percent higher than previously disclosed.

Of the 109 troops who have been diagnosed with brain injuries, 76 had returned to duty, officials said Monday.

“We are grateful to the efforts of our medical professionals who have worked diligently to ensure the appropriate level of care for our service members, which has enabled nearly 70 percent of those diagnosed to return to duty,” said Alyssa Farah, the Pentagon press secretary.

The latest tally, which has steadily grown since the Jan. 8 strike, drew a sharp contrast with the assertion by the Trump administration in the hours after the attack that no Americans were hurt. The number also underscored the unseen effects of traumatic brain injuries, which sometimes do not manifest symptoms for days or weeks but can have long-term physical or mental effects.