Nearly three dozen U.S. service members have been diagnosed with traumatic brain injuries following a Jan. 7 missile barrage on an Iraqi base housing coalition forces.

Up from the Defense Department’s initial report of zero injuries, a total of 34 troops experienced lingering headaches, dizziness, sensitivity to light, nausea and other symptoms after the assault on al-Asad Air Base, Pentagon spokesman Jonathan Hoffman told reporters on Friday.

“A lot of these symptoms, they are late developing,” he said. “They manifest over a period of time.”

See it: satellite images show rocket damage to Al Asad air base New satellite images show damaged and destroyed buildings at Al Asad Air Base in Iraq. Iran fired more than a dozen rockets at the base and another target in Iraq as tensions with the U.S. mounted recently. No casualties were reported.

While service members were initially screened for concussion following the blasts, more than 30 continued to experience symptoms throughout the last two weeks. In total, 16 were treated on site in Iraq, one was transported to Kuwait for treatment and has since returned to duty, while 17 were flown to U.S. facilities in Landstuhl, Germany.

As of Friday morning, Hoffman added, eight of those have returned to the U.S., either to be treated at Walter Reed National Military Medical Center in Bethesda, Maryland, or at their duty stations’ base hospitals.

Though TBIs have been the most numerous injury among American troops throughout the War on Terror, the reporting of the injuries at al-Asad prompted Defense Secretary Mark Esper last week to order a review of how a chain of command is notified of injuries in general.

“The reporting on symptoms vs. diagnosis, the reporting on that — we needed to have more clarity,” Hoffman said.

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Illness and injury among troops serving abroad is tracked in several ways, with different notification requirements. The defense secretary, for instance, would not be informed of troops showing symptoms or even being diagnosed with TBI, but an update would go out if they were flown off-site and thus taken out of the fight.

“The reporting did not come up until they were actually evacuating the area and taken to Germany,” Hoffman said of the al-Asad casualties.

As of Wednesday, according to the Associated Press, U.S. troops have resumed the anti-ISIS mission in Iraq.

Trump meets Iraqi counterpart, first since Soleimani strike U.S. President Donald Trump hinted that sanctions on Iraq were still a possibility in a bilateral meeting with Iraq’s president Wednesday, the first since a U.S. drone strike on Iraqi soil killed a top Iranian general, straining Washington-Baghdad ties.

Though tensions between the U.S. and Iran have settled, leaders have warned the the country’s activities in Iraq still pose a threat to U.S. troops.

“So I’ve been deployed for about nine months now and in the time that I’ve been there, we’ve had a couple of casualties that have been caused by conflict with ISIS on the ground, where some of our service members, certainly Iraqi Security Forces or Syrian Democratic Forces have suffered casualties, but most of the attacks against coalition forces in Iraq have come from elements of the Iranian threat network,” Maj. Gen. Alexus Grynkewich, deputy commander of Operation Inherent Resolve, told reporters on Wednesday.

In the wake of the U.S. killing of Iran’s Gen. Qassem Soleimani and Iran’s retaliation in Iraq, President Trump has called on NATO to contribute more forces to the anti-ISIS mission, though leaders have said no moves are underway to build up or draw down U.S. forces in the country.