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CNN  — 

Six US service members have been diagnosed with traumatic brain injuries as a result of attacks from Iran-backed groups in Syria last week.

Four US troops at the coalition base near al Hasakah that was attacked on March 23 by a suspected Iranian drone, and two service members at Mission Support Site Green Village attacked on March 24, have been identified as having brain injuries in screening since the attacks, Pentagon spokesman Brig. Gen. Patrick Ryder said Thursday.

“As standard procedure, all personnel in the vicinity of a blast are screened for traumatic brain injuries,” he said. “So these additional injuries were identified during post-attack medical screenings.”

Those screenings are ongoing, he added.

One of the service members has been transferred to Baghdad for further treatment, a US defense official familiar with the matter told CNN, noting that Baghdad has more advanced treatment options and better specialists than remaining on base in Syria.

The other five US service members who have been diagnosed with traumatic brain injuries are being treated at their facilities.

The news comes a week after the suspected Iranian drone struck a facility housing US personnel, killing an American contractor and wounding five service members. The US responded with precision air strikes on facilities associated with Iran’s Islamic Revolutionary Guards Corps, which Ryder said Thursday killed eight militants.

The US service members who were wounded in the attacks last week, Ryder said, “all are in stable condition.”

Of the five injured in the original attack on March 23, one other service member is receiving treatment in Germany, while two others and a contractor are being treated in Iraq, and two have returned to duty. The service member who was injured in attacks on March 24 is also receiving medical care and is in stable condition, Ryder said.

In 2020, more than 100 service members were diagnosed with mild traumatic brain injuries after an Iranian missile attack on the al Asad military base in Iraq. Chairman of the Joint Chiefs of Staff Gen. Mark Milley said at the time that symptoms take time to manifest.

“[I]t’s not an immediate thing necessarily – some cases it is, some cases it’s not,” he said. “So we continue to screen.”

Mild traumatic brain injuries, or concussion, is one of the most common forms of TBI among service members. But TBIs can also be debilitating; veterans described symptoms of dizziness, confusion, headaches, and irritability after sustaining TBIs, as well as changes in personality and balance issues.

On Thursday, Ryder reiterated US officials’ remarks last week that the US “will take all necessary measures to defend our troops and our interests overseas.”

“We do not seek conflict with Iran,” he said, “but we will always protect our people.”

This story has been updated with additional information.

CNN’s Oren Liebermann contributed to this report.