A U.S. F-16 fighter jet crashed Monday off South Korea during a routine training exercise after experiencing “an in-flight emergency,” the U.S. military said, adding the pilot ejected and was rescued.

The incident involving an F-16 Fighting Falcon assigned to the 8th Fighter Wing happened early Monday over the Yellow Sea, the U.S. Air Force said in a statement.

“The pilot ejected the aircraft. The pilot has been recovered by Republic of Korea Maritime Forces, awake and in stable condition,” the statement said, adding he would be evaluated further back at base.

“We are grateful for the safe recovery of our Airman by our ROK Allies and that the pilot is in good condition,” said Col. Matthew C. Gaetke, the 8th Fighter Wing’s commander, according to the statement.

The USAF said the cause of the in-flight emergency was unknown.

“The incident will be thoroughly investigated,” it said, adding that the pilot’s name and further word on his condition wouldn’t be released.

South Korea’s defense ministry declined to comment.

In May, a U.S. F-16 jet crashed during a routine training exercise in a farming area south of Seoul, South Korea. The pilot ejected safely and the accident caused no other casualties.

Washington is Seoul’s most important security ally and has about 28,500 troops stationed in South Korea to help protect it from nuclear-armed North Korea.

In neighboring Japan, the U.S. military announced last week that it was grounding its fleet of V-22 Osprey tilt-rotor aircraft following a deadly crash that killed eight U.S. airmen.