South Korean footballers were left dumbfounded at an international tournament in Indonesia when organisers played North Korea’s anthem instead.

Ahead of an AFC under-19 Championship qualifier against Jordan, at the Patriot Candrabhaga Stadium on the outskirts of Jakarta, the South Korean players lined up with their hands on their hearts.

But instead of Seoul’s hymn-like anthem “Aegukga”, North Korea’s national tune blared out, leaving them stony-faced and silent.

South Korea’s coaching staff told officials of the mistake, and while the correct song was then played, the team protested after the game on Monday evening.

Seoul’s football authorities said Tuesday that they will file a formal complaint with the Asian Football Confederation (AFC).

“This is the first time that the North Korean anthem was played instead of Aegukga at any official international match for any level of the national football team,” the Korea Football Association said in a statement.

The tournament’s local organising committee blamed the error on the audio operator in charge of playing the anthem.

“During the rehearsal, the South Korean anthem was played. But somehow the operator later picked the wrong song file,” Gatot Widagdo, media coordinator for the AFC U-19 Youth Championship, said Tuesday.

“The operator has (since) been replaced and we have apologised to South Korea verbally and in writing.” But he added that “somebody from the AFC should have monitored or guarded the control room“.

The mistake comes as a rapid diplomatic thaw takes hold on the peninsula, led by South Korea’s dovish President Moon Jae-in who has met with the North’s Kim Jong Un three times this year.

North and South Korea formed unified teams for some events at the Asian Games two months ago, also hosted by Indonesia, and reached the women’s basketball final.

But the democratic South Korea remains technically at war with the communist North Korea after the 1950-53 Korean War ended with an armistice instead of a peace treaty.

It is not the first time sports organisers have been stumped by Korean politics.At the 2012 Olympics, North Korea’s women footballers walked off the pitch ahead of a group match in Glasgow when they were introduced next to images of the South Korean flag