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Investigators who attended the scene at the Fort Pierce venue after emergency services were called to the Islamic Centre at 12.31am local time. The Floridian mosque was attended by Mateen who killed 49 people - in America’s worst mass shooting - at Pulse nightclub in June. The terrorist, who swore allegiance to ISIS, was killed in a shootout with police at the club. Moner Mohammad Abu Salha, who became a suicide bomber in Syria, also went to the mosque, according to American news channel WPEC.

WPTV · GETTY Orlando fire department has extinguished a fire at the Islamic Centre of Fort Pierce

The Sheriff’s Office is actively investigating this as an arson St Lucie County Sheriff’s Office

According to the station the FBI had twice investigated Mateen for terrorist ties, including links to Abu Salha. They, however, said it determined the connection between the pair to be “minimal” and not a “substantive relationship or threat at that time”. St Lucie County Sheriff’s Office said St Lucie County Fire District crews responded and successfully extinguished the fire. In a statement released, the Sheriff’s Office said: “A fire at any place of worship is alarming, regardless of the circumstances.

WPTV The mosque attended by the Orlando nightclub shooter has been set alight

Facebook The local Sheriff's Office suspects the fire was an arson attack

Facebook CCTV has been captured shows a suspect approaching the building before the fire starts

“Video captured at the Fort Pierce Islamic Centre shows an individual approaching the east side of the building just moments before a flash is seen and the fire starts. “The Sheriff’s Office is actively investigating this as an arson 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. “As soon as we are able, we will release the video if this incident and ask the public to assist us in identifying the person or persons responsible.” Authorities said it remains unclear if there were any ties to the 15th anniversary of the September 11 attacks.

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