A fire at the Florida mosque attended by the Pulse nightclub shooter is being investigated as arson, officials said Monday.

No injuries were reported.

Omar Mateen prayed at the Islamic Center of Fort Pierce before opening fire on a gay nightclub June 12 in an ISIS-inspired attack, killing 49 people and wounding 53 others. Moner Mohammad Abu Salha, an American jihadist who blew himself up in Syria, also attended the mosque.

The fire comes one day after the 15th anniversary of the 9/11 terror attacks.

"We all know the implications of the date and the time of year that this is, the 9/11 anniversary," St. Lucie County Sheriff's Major David Thompson told reporters. "Is that related? I would not want to speculate but certainly that is in the back of our minds."

Leaders of the mosque also had expected a large crowd to attend a Monday morning festival there to mark the start of the Eid al-Adha Islamic holiday.

“A fire at any place of worship is alarming, regardless of the circumstances,” a statement from the St. Lucie County Sheriff’s Office said. “Video captured at the Fort Pierce Islamic Center shows an individual approached the east side of the building just moments before a flash is seen and the fire starts.”

Mosque leaders had reported threats to the building – including arson – in June and had increased security, CBS12 reported.

One Facebook poster had threatened to “lock the doors when they are inside – and burn this place to the ground.”

The Sheriff’s Office is investigating with the assistance of the St. Lucie County Fire District, the Florida State Fire Marshall’s Office the Bureau of Alcohol, Tobacco and Firearms and the Federal Bureau of Investigations.

Authorities said they would release video of the incident shortly, but they were hoping to enhance the footage first.

"This is a terrible tragedy, not only for the Islamic Center, but for our community," Thompson said.

