The eight members of K-pop group Oh My Girl were detained at Los Angeles International Airport for 15 hours as U.S. Customs and Border Protection authorities quizzed them about their stay in California.

The teenagers were booked to perform at an event in Los Angeles and take part in a photo shoot, according to their managers, who have released a statement about the mix-up.

Translated, the note, obtained by the Los Angeles Times, reads: "As young women, they were mistaken as 'working women', which has recently been a big issue in the U.S."

The managers also disputed a visa issue, insisting the girls did not need a "performance visa" because they were participating in a promotional event.

A spokesman for U.S. Customs and Border Protection could not confirm or deny the group's claims.

"The Privacy Act prevents CBP from disclosing arrival/departure records of international travellers," he said.

The Oh My Girl stars and their handlers finally gave up attempting to convince the authorities that they weren't sex workers and flew home to South Korea. An investigation into the girls' lengthy detention is reportedly underway.