ASPEN, Colo. — In June the U.S. military began moving equipment and hundreds of troops back to a military base in Saudi Arabia that the U.S. deserted more than 15 years ago, according to two U.S. officials familiar with the deployment.

Over the coming weeks the deployment to Prince Sultan Air Base, intended to counter the threat from Iran, will grow to include fighter jets and Patriot long-range missile defense systems, the officials said. The Patriots have already arrived at the base and should be operational in mid-July, while the aircraft are expected to arrive in August.

Several hundred U.S. service members are already on site preparing the facility south of Riyadh, which is controlled by the Royal Saudi Air Force, a number that will grown to more than 500 after the arrival of an air squadron.

A recent satellite photo of activity at the Prince Sultan Air Base in Saudi Arabia. Planet Labs Inc.

The officials said the deployment focuses on defensive capabilities, with Patriot batteries for missile defense and the fighter jets intended to defend U.S. forces on the ground. But they acknowledged the aircraft could be used offensively as well.

The U.S. announced this increase of forces in the region in June, but did not say where the troops and equipment would be based.

The Pentagon declined to comment on the deployment to Prince Sultan air base. "U.S. Central Command continually works to manage our force posture in the region and will continue to do this in cooperation with our partners and allies in the region," said Pentagon spokesperson Lt. Col. Earl Brown on Thursday.

Central Command said in a statement Friday, “In coordination with and at the invitation of the Kingdom of Saudi Arabia, the Secretary of Defense has authorized the movement of U.S. personnel and resources to deploy to Saudi Arabia.”

“This movement of forces provides an additional deterrent, and ensures our ability to defend our forces and interests in the region from emergent, credible threats,” the Central Command statement said.

The U.S. military deployed troops and equipment to Saudi Arabia during the 1991 Gulf War, and U.S. aircraft based in the Kingdom were later used to enforce the no-fly zone over Iraq.

After the 1996 Khobar Towers bombing killed 19 U.S. airmen and injured 400 others, the U.S. military moved most aircraft and service members in Saudi Arabia to Prince Sultan Air Base, where they remained until the U.S. began Operation Iraqi Freedom in 2003. In April 2003, then-Secretary of Defense Donald Rumsfeld and the Saudi defense minister decided to withdraw all U.S. troops from the base and turn it back over to the Saudi government.

While Prince Sultan Air Base is an active facility, portions of the base will need an upgrade to accommodate the U.S. military, including reinforcing and expanding roads and runways, one U.S. official said. Base housing will also need updating, the official said, and the U.S. will build a medical facility. Many of the U.S. service members deployed there over the past few weeks are engineers preparing the base for the new mission.

This new deployment provides the U.S. military with another location in the region to counter a possible threat from Iran. The U.S. official said the base provides the U.S. with "strategic standoff" and "defensive depth" with Iran, meaning the ability to counter Iran from a distance while not being in range of Iranian missiles.

The officials described this deployment as expeditionary rather than permanent basing, with the new presence remaining there as long as tensions remain high with Iran.

The officials said Saudi Arabia has already agreed to pay some of the costs associated with having U.S. personnel and assets there.