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A total of 50 U.S. service members suffered traumatic brain injury from this month's Iranian missile attack on Iraqi bases hosting U.S. troops, the Defense Department said Tuesday.

Traumatic brain injury, or TBI, can include concussions. Of the 50 patients, 31 were treated in Iraq and have returned to duty, Army Lt. Col. Thomas Campbell, a spokesman for the Pentagon, said in a statement.

Last week, the Pentagon said 34 service members had been diagnosed with concussions and other traumatic brain injuries.

Of the 16 newly diagnosed patients, 15 have returned to duty in Iraq, Campbell said.

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Iran launched ballistic missiles at two bases in Iraq housing U.S. troops on Jan. 8 local time. The strike was in retaliation for the United States' killing of Iranian Maj. Gen. Qassem Soleimani, who was commander of its elite Quds Force, in a drone attack outside Baghdad's airport less than a week before.

No one was killed in Iran's strikes, and a day after U.S. forces were targeted, President Donald Trump said no one was hurt or killed.

The chief Pentagon spokesman, Jonathan Hoffman, said last week that a lot of TBI symptoms develop late and manifest themselves over time.

"The symptoms can get better. They can get worse," Hoffman said Friday. "So we may see those numbers change a little bit. This is a snapshot in time."

Damage at Ain al-Asad, an air base housing U.S. and other foreign personnel in the western Iraqi province of Anbar, on Jan. 13. Ayman Henna / AFP - Getty Images

The Centers for Disease Control and Prevention says on its website that some symptoms of concussions and other traumatic brain injuries can appear right away but that other symptoms may not be noticed for days or months.

One of the new cases involved a service member transported to Germany for further evaluation and treatment, bringing the total taken there to 18. That person had been taken to Germany "for other health reasons and has since been diagnosed with a TBI," Campbell said.

Last week, another Pentagon spokesman said eight U.S. service members who were sent to Germany were then taken to the United States.

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Campbell's statement Tuesday said there was no information whether anyone else has returned to the U.S. A service member who had been taken to Kuwait for treatment has since returned to duty, he said.

Hours after Iran launched missiles against U.S. forces, Iran's armed forces shot down a Ukrainian passenger plane shortly after takeoff from Tehran's airport in an incident that Iranian officials blamed on "human error" and that Iran's president has called an "unforgivable mistake."

All 176 people aboard Ukraine International Airlines Flight PS752 were killed, including many Iranians and Canadians.