SEOUL, June 12 (Reuters) - Fans of K-Pop supergroup BTS gathered in the heart of the South Korean capital Seoul on Monday to celebrate the 10-year anniversary of the boy band's debut.

Although the group is on hiatus with two of the members currently doing mandatory military service, many of their loyal global fanbase called "ARMY" still gathered in Seoul this week.

The seven-member group has gained a huge international following after breaking ground for K-Pop's global success including in the U.S. music charts and industry awards.

Landmarks such as Seoul City Hall and Namsan Tower were lit purple, BTS' signature color, while dozens of fans from France, Mexico, and elsewhere came to enjoy the sights.

"I came to Korea last week and I am very surprised and excited to see the Namsan Tower purple," said Rita, a 20-year-old student from France who has been an ARMY since 2018.

Organizations and businesses are also joining the celebration, with the city of Seoul working with BTS' management agency HYBE to set up a tour of landmarks associated with BTS. South Korea's postal service released special commemorative stamps for BTS' debut anniversary.

Companies such as Hyundai Department Store, Lotte Shopping unit Lotte Cinema, and S-Oil have introduced special offers or events.

The celebrations are expected to hit a climax on Saturday when BTS leader RM is expected to meet fans - followed by fireworks near the Han River, which bisects Seoul.

"Thank you for teaching us a little, or maybe even too much, about happiness and love," member JungKook told fans in a Twitter message on Sunday. "I want to keep walking with you all for the next 10 years as well".