Atleast 11 American troops were wounded in an Iranian assault on an Iraqi base where American soldiers were stationed, said U.S. Central Command on Thursday, although the U.S military had previously reported that there had been no casualties.

“While no US 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,” US Central Command spokesman Captain Bill Urban said in a statement.

Most of the 1,500 US troops at the base had been sent to their bunkers at the time of the attack, with an advance warning from authorities.

According to previous reports from the US military, the attack caused considerable material damage but no casualties.

In the morning after the shot, US President Donald Trump said that “no American was injured 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 vast Ain al-Asad airbase in western Iraq, Iran’s missiles also struck a base in Arbil, housing American as well as other foreign troops deployed in a US-led coalition battling the members of the Islamic State jihadist group.

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