WASHINGTON >> Three service members were killed, including two Americans, and a dozen more were injured when a barrage of rockets were fired at a military base in Iraq, U.S. officials said today.

One of the officials said five service members were seriously wounded and evacuated from the Camp Taji base and seven others were still being evaluated. Buildings on the base were in flames. Several other U.S. officials confirmed that U.S. troops had been killed and injured, but did not provide numbers. The officials spoke on condition of anonymity to give details of the attack ahead of a public announcement.

Army Col. Myles Caggins, a U.S. military spokewman in Iraq, said on Twitter that more than 15 small rockets hit Iraq’s Camp Taji base. He provided no details. Another U.S. official said that as many as 30 rockets were fired from a truck launcher, and 18 hit the base.

Officials did not say what group they believe launched the rocket attack, but Kataib Hezbollah or another Iranian-backed Shia militia group is likely.

Camp Taji, located just north of Baghdad, has been used as a training base for a number of years. There are as many as 6,000 U.S. troops in Iraq, training and advising Iraqi forces and conducting counterterror missions.

Kataib Hezbollah was responsible for a late December rocket attack on a military base in Kirkuk that killed a U.S. contractor, prompting American military strikes in response.

That in turn led to protests at the U.S. embassy in Baghdad. They were followed January 3 by a U.S. airstrike that killed Iran’s most powerful military officer, Gen. Qassem Soleimani, and Abu Mahdi al-Muhandis, a leader of the Iran-backed militias in Iraq, of which Kataib Hezbollah is a member.

Kataib Hezbollah been designated a “foreign terrorist organization” by the State Department since 2009.

Syrian opposition activists and a war monitor reported later an airstrike that targeted Iranian militia positions along the Iraq-Syria border.

The Syrian Observatory for Human Rights reported 10 airstrikes carried out by three unidentified aircraft that targeted pro-Iran militias in the Boukamal region in eastern Syria, near the border with Iraq. The Britain-based Observatory which monitors the Syria war through a network of activists on the ground said at least 10 explosions were heard in the region but said there was no immediate word on casualties.

U.S. officials said the strike was not related to the Taji base strike at all. But, it was not immediately clear who conducted the attack.

Syrian activist Omar Abu Layla said the unidentified airstrike targeted Iranian militia positions in the Boukamal region.

Syrian state-run media also reported an aerial attack in the Boukamal region near the Iraqi border that caused material damage.