Four mid-ranking executives from China Southern Airlines are under police investigation for corruption, the airline confirmed on its micro blog.

China Southern said it noticed irregularities and reported them to the police after an internal audit.

The carrier did not release the identities of the executives or details of their alleged irregularities.

However, a source said that Yu Siyou, deputy director of the airline’s marketing management committee, was allegedly one of the four executives.

The marketing management committee supervises departments, including sales and marketing.