Oh My Girl -- Korean Group Angry at U.S. Customs ... We're Not Prostitutes!

A Korean girl group called Oh My Girl was detained at LAX, their record label claiming they were wrongly targeted as underage prostitutes, but our sources say the group was trying to enter the country under questionable circumstances.

The girls arrived at LAX Friday from South Korea but got stopped at U.S. Customs. Their record label claims the feds noticed the girls were traveling with costumes and jumped to the conclusion they were prostitutes. A label rep says they were held for 15 hours and booted back to Korea.

But our sources say, what really happened was that the girls tried entering on a visitor visa. When customs officials noticed they were traveling with a ton of luggage that included costumes and other markers, they started asking questions and realized the group was here to perform.

Our sources say the proper papers would have been a Performer Visa, which they didn't have. So the girls were held in the customs office for around 10 hours until they could catch a flight home.

The girls were supposed to perform at the Beverly Hilton Hotel Saturday at an event ... Unforgettable, 2015.

At least their trip was unforgettable.