South Korea's Army is seeking to tighten the supervision of its troops assigned to the US Forces Korea, a military official here said Monday, following the recent indictment of five soldiers on charges of absence without leave.

Currently, 3,400 Army troops work as part of the Korean Augmentation to the US Army, better known as the KATUSA.

The South Korean Army's control over them has been relatively loose as they are based in US military installations.

"We are thinking of increasing the Army staff supervising the KATUSA staff or carrying out unannounced checks on whether they are at the posts of responsibility or absent without leave," the official told Yonhap News Agency on condition of anonymity.

"We are exploring such measures, but no definitive decision has been made as some options involve budget approval," he added.

Last month, the military prosecution indicted five KATUSA sergeants who worked at Camp Casey in Dongducheon, 40 kilometers north of Seoul, on charges of leaving their posts without permission for up to one month. They were not detained.

Calls have long persisted that there should be an increase in the number of military staff overseeing the management of the KATUSA program. Currently, one senior officer is known to handle 60 to 80 KATUSA soldiers.

Seoul's defense ministry spends 10 billion ($8.82 million) each year on the KATUSA program.