The FBI is investigating the cybersecurity issue that thwarted credit card transactions and affected computerized systems throughout MGM Resorts International properties.

“MGM has requested assistance, and we are providing it,” Special Agent Mark Neria, of the bureau’s Las Vegas field office, said Tuesday morning.

MGM did not refer to the matter as a cyberattack, and the company did not elaborate on what systems were affected or how the incident may have occurred.

Neria declined to comment further on the issue, citing an ongoing investigation.

On Monday, the company directed customers seeking hotel reservations to call properties directly because the online reservation system was inoperative. They remained inoperative Tuesday morning.