Several American troops stationed in the Middle East have reported symptoms of traumatic brain injury following rocket and drone attacks launched by Iran proxies over the past week, according to two U.S. officials with knowledge.

“There have been a few reports of TBIs as well as some minor injuries from service members,” said one of the U.S. officials, using the acronym for “traumatic brain injuries.”

However, the injured service members have all been returned to duty, added the official, who like others interviewed for this story was granted anonymity because they were not authorized to speak publicly.

More than 20 service members have reported minor injuries so far as a result of the Iran-backed attacks on U.S. positions in Iraq and Syria, according to a Defense Department official.

NBC News first reported the number of injuries.