Chinese authorities have reportedly detained several representatives of Australian casino operator Crown Resorts for as yet unknown reasons.

On Friday, the Australian Financial Review reported that Chinese authorities had detained “at least 18” Crown staffers, including three Australian nationals, one of whom was said to be a “senior Crown executive.”

The AFR quoted a Crown spokesperson saying only that the company “believes that a number of our employees in China are being questioned by local authorities” but had no other details to offer. An Aussie government spokesperson said it was “aware” of the reports and was trying to confirm specifics with the relevant Chinese authorities. The two nations have an agreement that requires each country to confirm that it’s holding the other’s citizens within 72 hours of their detention.

The AFR said most of the affected staffers were based in China as part of Crown’s local sales and marketing team. Chinese law prohibits advertising gambling services on the mainland but casino operators are permitted to promote their resorts’ non-gaming tourism offerings.