The countries have long worried about being sucked into regional war as they juggle relations with Washington, their security guarantor, while seeking to improve ties with Tehran.

The Pentagon already had begun taking measures to strengthen its firepower in the Middle East and protect U.S. bases there.

Iran retaliated against the U.S. on Monday, launching missiles at a U.S. base in Qatar, according to a U.S. defense official and a statement from the Qatar foreign ministry. The missiles targeted Al Udeid Air Base outside Doha and were intercepted by air defenses before they could strike the base,