The septet has become a global cultural phenomenon, selling out stadiums and dominating charts while raking in billions for South Korea's economy and building an international legion of fans known as ARMY.

But all able-bodied South Korean men must serve at least 18 months in the military, and after a years-long debate about whether BTS deserved an exemption, Jin, the oldest member of the group, began his service in December, with J-Hope starting basic training in April.

SUGA "has started his alternative service from today," an official with their agency HYBE told AFP.

He will work as a social service agent, the Yonhap News Agency reported, saying SUGA had been "ruled unfit for the regular combat duty."

While all able-bodied men must serve in the military, people with health issues may be assigned to 21 months of alternative services, which can include working in an office for a municipal government.

The reasons for the decision on Suga have not been disclosed, however it is believed to be related to shoulder surgery he had in 2020, Yonhap said.

On Friday, SUGA told fans: "I have made it this far thanks to you all."

"The time has come," to begin my service, he wrote on social media.

"I will return after diligently fulfilling my service... Let's all meet again in 2025!" he added.

- 'The king will return' -

Fans of SUGA -- real name Min Yoon-gi -- vowed that the alternative service would not be a hinderance to his career.

"Dearest Yoongi, Stay safe, stay healthy, stay well... We'll be right here waiting for you. Yoongi is worth the wait. The king will return," one fan wrote on X, formerly Twitter.

"2 years apart is nothing compared the lifetime we'll have together," another wrote.

HYBE also asked fans not go to SUGA's new place of duty, which could be anything from a metro station to a municipal office.

"We ask fans to refrain from visiting SUGA's work location during its alternative service period. We ask that you only give a warm send-off and encouragement to SUGA from your heart," is said in a statement.

The spectre of conscription has long hovered over BTS, with many experts pointing to South Korea's mandatory military service for the septet's current break.

The band had initially cited exhaustion and the pressures of stratospheric success when they initially announced they would go on "hiatus" last year, saying they were taking a break to focus on their solo careers.

HYBE said this week that all seven members of BTS would renew their contracts with the agency.

The company did not disclose details of how long the new contracts were or when they would expire, but the latest announcement indicates that all seven members of the group will likely remain with the label even after they have completed their military service.

Analysts have questioned what the future holds for the group after all seven members complete their military service.

Some male K-pop stars have struggled to resume their careers after military service in a cut-throat industry where artists are easily replaceable.