The Orlando shooter responsible for the massacre of 49 people at a gay club in Florida last month had been taunted for being a Muslim, documents released on Monday revealed.

While working as a security guard at the St Lucie County courthouse in Fort Pierce, Omar Mateen was reportedly insulted by his fellow workers.

According to the Orlando Sentinel, he was called "evil" and a member of a "blood sucking cult". One co-worker said "We need to nuke all... Muslims" and another branded him "a f****** terrorist".

Mateen made the allegations in a complaint filed in 2013. He had been investigated by the FBI after claiming to have ties to the Boston Marathon bombing suspects and the Fort Hood shooter, but he told officers he'd made it up in an attempt to stop the taunts.

He was initially placed on an FBI terrorist watch list but investigators concluded he was not a terrorist.

He wrote in his complaint: "I love the United States. I'm 1000% pure American. I'm ready to give up my life defending the United States."

Mateen was shot dead by police after the June 12 massacre which was the worst mass shooting in modern US history.

Transcripts released by the FBI showed that he had called himself an "Islamic soldier" in calls with police during the three-hour siege.

In a 911 call, he pledged allegiance to the leader of Islamic State.