"The jet crashed into the waters after taking off from an air base in Gunsan, 178 kilometers south of Seoul," the agency reported, referring to waters in the Yellow Sea.

The pilot ejected from the jet and was rescued, Yonhap reported.

South Korea's defence ministry declined to comment. United States Forces Korea, which oversees American soldiers based in the South, was not immediately available to confirm the report.

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

Washington is Seoul's key security ally and stations about 28,500 troops in South Korea to help protect it from the nuclear-armed North.

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