The US Embassy in Saudi Arabia has issued an urgent update, warning it is tracking reports "of threats against locations where American citizens gather". These include hotels, US businesses and educational institutions, the embassy in the Gulf state said, as the Iran war continues to rage.

The embassy has warned that such "gathering points" may become potential targets for attacks and advises Americans to "excercise increased caution". All US citizens and employees in Saudi Arabia are being warned to take shelter due to the possibility of strikes. They are also advised to have a supply of essential items, including food, water and medications.

Americans in Saudi Arabia are being urged to "remain in your residence or another structure" until further notice due to the possibility of attacks. They should also "stay away from windows" while taking shelter.

The US Embassy in Riyadh said: "Essential employees remaining will continue under shelter-in-place status and are advised to avoid the U.S. Embassy, U.S. Consulate Dhahran, and hotels.  We recommend all Americans in the Kingdom do the same until further notice.  To the extent possible, remain in your residence or another structure, and stay away from windows.

"We are tracking reports of threats against locations where American citizens gather.  We advise U.S. citizens that hotels and other gathering points including U.S. businesses and U.S. educational institutions may be potential targets."

Although some airlines have suspended flights, there are some commercial departure options available to Americans. However, they should only opt for these flights if it is safe to do so.

The embassy said: "If you want to leave the Middle East, the U.S. government is ready to assist by providing you the latest information about the departure options available. President Trump, Secretary of State Rubio, and the Department of State have no higher priority than the safety and security of American citizens.

"If you choose to not take advantage of available commercial departure options, you should be prepared to shelter in place in a secure location within your residence or another safe building."

They added: "We encourage U.S. citizens to depart Saudi Arabia via commercial flights if you can do so safely. Saudi airspace remains open with frequent air traffic restrictions to address continued missile and drone threats.  Riyadh, Jeddah, and Dammam airports remain open and operational, but travelers are advised to check their flight status directly with the airline due to possible delays and cancellations."

The warning comes as the UK sends more troops and air defence systems to the Middle East. Meanwhile, another US aircraft carrier, the USS George HW Bush, is expected to head to the Middle East.