The U.S. military has moved some aircraft and ships from bases in the Middle East that may be vulnerable to any potential Iranian attack, two U.S. officials told Reuters on Wednesday.

The moves come as President Donald Trump kept the world guessing whether the United States would join Israel's bombardment of Iran's nuclear and missile sites, as residents fled its capital on the sixth day of the air assault.

Separately, the U.S. embassy in Qatar issued an alert on Thursday temporarily restricting its personnel from accessing the Al Udeid Air Base, the largest U.S. military installation in the Middle East, which is located in the desert outside Doha.

The embassy told personnel and U.S. citizens in Qatar to step up vigilance in "an abundance of caution and in light of ongoing regional hostilities".

The two U.S. officials, who spoke on condition of anonymity, said the move of aircraft and ships was a part of plans to protect U.S. forces, but declined to say how many had been moved and where to.

One of the officials said aircraft that were not in hardened shelters had been moved from Al Udeid base and naval vessels had been moved from a port in Bahrain, where the military's 5th fleet is located.

"It is not an uncommon practice," the official added. "Force protection is the priority."

Reuters was first to report this week the movement of a large number of tanker aircraft to Europe and other military assets to the Middle East, including the deployment of more fighter jets.

An aircraft carrier in the Indo-Pacific is also heading to the Middle East.

Israel launched an air war on Friday after saying it had concluded Iran was on the verge of developing a nuclear weapon. Iran denies seeking nuclear weapons.

Iran has conveyed to Washington that it will respond firmly to the United States if the latter becomes directly involved in Israel's military campaign, the Iranian ambassador to the United Nations in Geneva said on Wednesday.

(Reuters)

US moves military assets, limits access to its largest Middle East base