Three men were killed in a shooting outside the Islamic Center of San Diego on Monday, while two teenage suspects were later found dead from apparent self-inflicted gunshot wounds, according to police.

According to Reuters, San Diego Police Chief Scott Wahl said the attack happened shortly before midday at the mosque in the Clairemont district of the city.

Authorities said the victims included a security guard who may have helped prevent further casualties.

Police said all children attending the day school connected to the mosque were safely accounted for after the shooting.

Wahl said investigators are treating the incident as a possible hate crime, although no motive has yet been confirmed. The FBI has joined the investigation.

“We have never experienced a tragedy like this before. It is extremely outrageous to target a place of worship,” said Taha Hassane, imam and director of the Islamic Center.

Police later discovered the bodies of two suspects, aged 17 and 19, inside a vehicle nearby, and believe both died from self-inflicted gunshot wounds.

Law enforcement officers flooded the scene within minutes of reports of an active shooter. Television footage showed heavily armed police surrounding the mosque complex.

The attack comes ahead of Eid al-Adha and the annual Hajj pilgrimage, during a period of heightened concern among Muslim communities following tensions and conflict in the Middle East.