A police officer has been arrested at a hotel in Co Antrim.
It came as the Police Service of Northern Ireland (PSNI) responded to a report of an incident at the hotel in Ballymena on Thursday.
Off-duty police officers had been in attendance at the event.
A criminal investigation has been launched, as well as a professional standards department misconduct probe.
In a statement Superintendent Claire McGuigan said: “Police responded to a reported incident at an event in a hotel in Ballymena on September 21 which off-duty police officers were attending.
“One serving police officer was arrested in connection with the incident and he is currently in custody.
“A criminal investigation has commenced and a professional standards department misconduct investigation is now running in parallel.”
She added: “The Police Service expects its officers and staff to behave professionally, ethically and with the utmost integrity at all times.”