WASHINGTON, Jan. 16 (Xinhua) -- Eleven U.S. troops were treated for concussion symptoms as a result of last week's Iranian missile attack on U.S. military base in Iraq, the U.S. military said Thursday in a statement.

"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," Captain Bill Urban, spokesman for U.S. Central Command, said in a statement.

After last week's attack in western Iraq, the Pentagon initially said that no casualty was reported.

The statement said some service members received "follow-on screening" as a measure of caution and consequently the symptoms were found.

Eight persons were transported to Germany and three sent to Kuwait for further screening, reported CNN Thursday, citing anonymous U.S. military official.

CNN also reported that an anonymous U.S. defense official claimed that the symptoms of the injured troops emerged "days after the fact."

Seeking revenge for the killing of Iranian senior commander Qassem Soleimani by a U.S. drone strike on Jan. 3 in Iraq, Iran retaliated on Jan. 8 by launching ballistic missiles on military bases housing U.S. troops in Iraq's western province of Anbar and near the city of Erbil, capital of the semi-autonomous region of Kurdistan.

More than 5,000 U.S. troops are deployed in Iraq to support the Iraqi forces in the battle against Islamic State militants.