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ST. LUCIE COUNTY, Fla. —Authorities said Monday morning that an arson investigation was underwayafter the Florida mosque that Orlando nightclub shooter Omar Mateen attended before his death caught fire overnight.

The fire was reported at about 12:31 a.m. when a 911 caller saw flames coming from the Islamic Center of Fort Pierce, located in the 1100 block of West Midway Road, St. Lucie County Sheriff’s Office spokesman Maj. David Thompson said.

RELATED: A partial transcript of Omar Mateen’s 911 calls during the Orlando shooting has been released

The cause of the fire is under investigation, but so far there is no indication whether it was arson or accidental, he said.

The fire happened hours after the 15th anniversary of the 9/11 attacks that killed nearly 3,000 people and injured 6,000 others.

It also happened exactly three months after the Pulse nightclub massacre that killed 49 and injured 53 others.

Mateen, who attended the Islamic Center, was killed as SWAT team members breached the building to rescue victims trapped inside.

It is too early in the investigation to connect 9/11 or the Pulse attacks to the fire, Thompson said.

“You know, that’s always a conclusion that someone could jump to,” he said. “As I said, at this time we’re unsure even the cause of the fire is, so I wouldn’t want to speculate whether or not this was related or unrelated.”

No injuries were reported in connection with the fire.

The extent of the damage done to the mosque was not immediately released.