Washington, July 20 -- With Iranian military threats in mind, the United States is sending American forces, including fighter aircraft, air defense missiles and likely more than 500 troops, to a Saudi air base that became a hub of American air power in the Middle East in the 1990s but was abandoned by Washington after it toppled Iraqi strongman Saddam Hussein in 2003.

The Saudi Foreign Ministry announced the basing agreement Friday without mentioning details.

Senior American defense officials said some U.S. troops and Patriot air defense missile systems have already arrived at Prince Sultan Air Base, south of Riyadh, where the troops have been preparing for the arrival of aircraft later this summer as well as additional troops. The offi...