Ain al-Asad, one of the air bases attacked by Iran on Wednesday, is a hub for hundreds of U.S. personnel in Iraq.
The base, a sprawling complex about 110 miles northwest of Baghdad, houses about 1,500 members of the U.S. military and the U.S.-led coalition fighting the Islamic State militant group, according to The Associated Press. It's in the western Anbar desert of Iraq.
Full coverage of the crisis with Iran
It was not immediately known whether there were any deaths or injuries. Like other large bases overseas, Ain al-Asad is "full of places where troops can take cover," NBC News foreign correspondent Richard Engel reported.
Let our news meet your inbox. The news and stories that matters, delivered weekday mornings.
In addition to the 1,500 U.S. and coalition forces, about 70 Norwegian troops were at Ain al-Asad at the time of the attack, according to the AP.
Download the NBC News app for breaking news and full coverage of the Iran crisis
Both the president and the vice president have traveled to Ain al-Asad in recent years.
In December 2018, President Donald Trump made a surprise Christmastime visit to U.S. troops, flying in on a darkened Air Force One with first lady Melania Trump. It was his first time in an active combat zone while in office.
Vice President Mike Pence and Karen Pence also paid an unannounced visit to Ain al-Asad just before Thanksgiving last year and served a turkey lunch to U.S. forces.
"Here at all al-Asad air base, you prove every day what the world knows: The armed forces of the United States are the greatest force for good that the world has ever known," the vice president told troops at the time.
By attacking Ain al-Asad, Iran was retaliating for the killing of Qassem Soleimani, a top Iranian general, in a U.S. airstrike last week. Iran fired more than a dozen ballistic missiles at Ain al-Asad and another Iraqi air base housing U.S. forces.
An estimated 5,000 U.S. troops are stationed throughout Iraq.
Ain al-Asad was the first base used by U.S. troops after the 2003 invasion Iraq, which led to the downfall of dictator Saddam Hussein.