Some Indonesian employees at the Korea Aerospace Industries have been barred from leaving South Korea on suspicions they were trying to steal secrets about KF-21 fighter technology.

KAI reported the employees to the Defense Acquisition Program Administration last month after becoming suspicious of an attempted leak.

The administration, a public affiliate of the Ministry of National Defense, said that an investigation is underway to determine if the information the employees are suspected of storing includes military secrets.

The employees are being investigated by a joint team composed of the Defense Counterintelligence Command and the National Intelligence Service, according to the Defense Counterintelligence Command on Friday.

The joint team is looking into the possibility the employees may have had inside help at KAI. Other details are being withheld while the investigation is underway.

The suspected leak sparked diplomatic concerns as some of the KF-21 technology that KAI received from the US reportedly has not yet been cleared for export.

Indonesia failed to pay for its share of the project launched in 2015 for co-developing KF-21 fighters with South Korea.

Indonesia agreed to pay for 20 percent of the joint project, or 1.7 trillion won ($1.3 billion) -- later discounted to 1.6 trillion won -- by June 2026 on the condition that 48 of the aircraft are manufactured in Indonesia. The amount of the country’s outstanding installments to date stands at 1 trillion won.