A gunman killed at least five and wounded nine others at a nightclub in Playa del Carmen, Mexico on Monday, according to CBS News.

A Mexican police offer who reported the incident chose to remain anonymous, as he wasn’t authorized to release details about the ongoing investigation. Little information is public at this time. Witnesses are being interviewed and the motive is still unclear, he said.

The shooting took place at The Blue Parrot nightclub at approximately 2:30 a.m., where a BPM electronic music festival event was being held. The festival’s official Facebook page posted a statement on Monday, confirming four deaths and twelve injuries.

UNO TV – a partner of CBS – reported that, according to Quintana Roo state prosecutor Miguel Ángel Pech Cen, none of the victims were American. However, Fox News reported that two Americans were injured.

The music festival organizers added that “three members of the BPM security team were among those whose lives were lost while trying to protect patrons inside the venue.” According to Fox News, four, not three, security personnel were killed.

Prosecutor Ángel Pech Cenalso told UNO TV that the attack is not believed to be related to terrorist activities.

Latest reports indicate that four people have been detained, although it is not clear whether the shooter is definitely among them.