An F-35A fighter operated by South Korea's Air Force made an emergency landing during a training session Tuesday due to avionic system issues, with its pilot having emerged unscathed, officials said.

The radar-evading jet made the belly landing on a runway at an air base in Seosan, 151 kilometers south of Seoul, at 12:51 p.m. after the issues caused the landing gear to momentarily malfunction, the officials said.

The pilot walked away unscathed, they added.

Before the landing, the Air Force mobilized a fire engine to apply special foam on the runway, which prevented the jet's fuselage from sustaining any serious damage.

It apparently marks the first known belly landing ever reported since the US began exporting F-35A fighters to foreign countries, an informed military source said.

South Korea's Air Force and the US military plan to initiate a joint investigation into what went wrong with the fighter manufactured by the US defense firm Lockheed Martin.

The Air Force will suspend all of its F-35A fighters pending the probe, the officials said.

It has so far received more than 30 F-35A jets from the United States under a plan to deploy a total of 40 units.

The F-35A is the fighter's air force variant, while the F-35B and F-35C are for marine and aircraft carrier-based operations, respectively. (Yonhap)