The Pentagon said Friday that 34 U.S. service members have been treated for concussion symptoms and traumatic brain injuries after the missile attack earlier this month by Iran on a U.S. airbase in Iraq. About half of those treated have returned to active duty, while others are still being treated.

According to the Pentagon, nine U.S. service members are being treated in Germany and eight have been transferred to the U.S. Being transferred to the U.S. does not necessarily mean their injuries are more severe; instead, they are receiving treatment at their home base, CBS News' David Martin reports.

One service member who was evacuated to Kuwait has returned to Iraq, and all the service members who were treated in Iraq have returned to active duty.

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U.S. officials initially said no one was injured in the January 8 strike on Al Asad airbase, which Iran launched in retaliation for the strike that killed Iranian Major General Qassem Soleimani. But the Pentagon said on January 16 that 11 U.S. service members were being treated for concussion symptoms and were being screened for traumatic brain injuries.

A Pentagon spokesman said Friday that Defense Secretary Mark Esper has ordered a review of reporting procedures since Esper did not find out about these injuries until days after the attack.

Speaking in Switzerland earlier this week, President Trump appeared to downplay the injuries. When CBS News' Weijia Jiang asked about the discrepancy between the initial report and later accounts of injuries, Mr. Trump replied, "I heard that they had headaches and a couple of other things, but I would say that, and I can report, it is not very serious."

Pressed further, Mr. Trump said, "I don't consider them very serious injuries, relative to other injuries that I've seen. I've seen what Iran has done with their roadside bombs to our troops, I've seen people with no legs and with no arms, I've seen people that were horribly, horribly injured, and that area, that war, in fact, [in] many cases, put those bombs, out there by Soleimani, who is no longer with us. I consider them to be really bad injuries. No, I do not consider that to be bad injuries, no."

-David Martin and Weijia Jiang contributed to this report.