The U.S. Embassy in Qatar warned American citizens to "shelter in place until further notice." The embassy said in its June 23 alert that it was acting "out of an abundance of caution" but gave no other details. Qatar is home to the Al Udeid Air Base, the largest U.S. air base in the Middle East.

The US and UK governments told citizens based in Qatar to lie low after Iran vowed to retaliate against an American attack on its nuclear facilities.

The U.S. embassy in Qatar emailed a message to U.S. citizens in the Gulf country on Monday recommending that they shelter in place until further notice. The message noted the recommendation was "out of an abundance of caution" and offered no further information.