At least 11 American troops were injured in an Iranian attack on an Iraqi base where American soldiers were deployed, U.S. Central Command said Thursday. The U.S. military had previously maintained there were no casualties.

“While no U.S. service members were killed in the Jan. 8 Iranian attack on al-Asad air base, several were treated for concussion symptoms from the blast and are still being assessed,” U.S. Central Command spokesman Capt. Bill Urban said in a statement.

At the time of the attack, most of the 1,500 U.S. soldiers at the base had been tucked away in bunkers, after advance warning from superiors.

The strike caused significant material damage but no casualties, according to previous reports from the U.S. military.

U.S. President Donald Trump also said on the morning following the volley that “no American were harmed in last night’s attack.”

However, Urban said that “in the days following the attack, out of an abundance of caution, some service members were transported from al-Asad air base.”

“At this time, eight individuals have been transported to Landstuhl, and three have been transported to Camp Arifjan,” he said, referring to Landstuhl Regional Medical Center in Germany and Camp Arifjan in Kuwait.

In addition to the sprawling Ain al-Asad air base in western Iraq, Iran’s missiles also targeted a base in Irbil, housing both American and other foreign troops deployed in a U.S.-led coalition fighting the remnants of the Islamic State jihadi group.

“When deemed fit for duty, the service members are expected to return to Iraq following screening,” Urban said.