BTS star Jin started his mandatory South Korean military duty on Tuesday, the band's first member to enlist since a hiatus announcement this year left fans heartbroken over the K-pop juggernaut's uncertain future.

The septet is widely considered the country's biggest-ever cultural phenomenon. They've sold out stadiums around the world and dominated the charts while raking in billions and building a global legion of fans known as ARMYs.

But all able-bodied men in South Korea must serve at least 18 months in the military, and while there was a years-long debate about whether BTS deserved an exemption, they confirmed in October that all members will enlist.

A black van believed to be carrying BTS singer Jin arrives at the main gate of a military training unit in Yeoncheon

Jin, whose full name is Kim Seok-jin, reported to a frontline boot camp in Yeoncheon on Tuesday to begin his five-week training, kickstarting 18 months of military service.

He was riding one of the black vans that arrived in a row around 20 minutes before a 2pm (5am GMT) deadline, according to BTS's agency HYBE.

Hundreds of media personnel and BTS fans packed an intersection in front of the boot camp's main gate, where a sign reads "A cradle for top class combat soldiers".

Fans hold pictures of BTS singer Jin in front of a military training unit in Yeoncheon

"We have mixed feelings today because on one hand, it's normal that he does this enlistment because it's an obligation anyway for any Korean men," said Veronique, a 32-year-old fan from Indonesia.

"But on the other hand we cannot see him for a minimum of 18 months ... Happy but also sad but also proud," she said.

The location of Jin's boot camp close to the border with North Korea, with which the South remains technically at war, has sparked local media speculation that he is expected to be deployed to a "frontline unit" after training.

Fans were stunned in June when BTS revealed they were going on hiatus, citing exhaustion and pressure as well as the desire to pursue solo careers.

But analysts said the announcement was timed because of the compulsory military duty.

The group will reunite around 2025, when its seven members have completed their service.

Nimah Mustafa, a 20-year-old fan in Dubai, said: "(Jin's absence) will be like a huge... void for me."

BTS pictured together in New York in 2020

South Korea exempts some elite athletes, such as Olympic medallists, and classical musicians from duty, but pop stars do not qualify.

However, BTS have already benefited from a 2020 revision to the conscription law that raised the enlistment deadline for some entertainers from age 28 to 30.

Jin, the oldest member of BTS, turned 30 on 4 December.

Since their debut in 2013, BTS have been widely credited with doing more than any diplomat or other celebrity to boost the image and soft power of South Korea, today considered a global cultural powerhouse.

They have been invited to speak at the United Nations, and to meet US President Joe Biden at the White House. They are also official ambassadors to bring the 2030 World Expo to Busan, South Korea.

The South Korean government has credited BTS with bringing billions of dollars into the economy.

But despite that success, a draft proposal to grant them service exemptions proved too controversial and never made it through parliament.

Source: AFP