The 15 male ballet students groaned as they strained to do the splits and laughed with relief after their teacher counted to five and let them relax.

Once a week, a group of South Korean soldiers near the Demilitarized Zone (DMZ) that divides the Korean peninsula trade army boots for ballet shoes in a class intended to ease the stress of guarding the world's most heavily fortified border.

"There's a lot of tension here since we live in the unit on the front line, which makes me feel insecure at times," said Kim Joo-hyeok, a 23-year-old sergeant doing his nearly two years of military service that is mandatory for South Korean men.