Orlando shooting: Police hunting for possible accomplices of gay nightclub attacker Omar Mateen

Authorities said they do not believe there is any imminent threat to the public

(AP)

Police are hunting for possible accomplices of the Orlando attacker as investigations continue into possible motives behind the worst mass shooting in US history.

Local reports in Florida claimed an arrest was imminent on Tuesday, with WFTV News claiming at least one person is believed to have known of Omar Mateen’s plans.

There were initial reports of other accomplices or suspects in the shooting but investigators said they do not believe anyone was working with the gunman at the club.

The suspect's father says his son reacted angrily to seeing gay men kissing in Miami a couple of months ago (Myspace)

US Attorney Lee Bentley said: “We do not know yet whether anyone else will be charged in connection with this crime, but have no reason to believe that anyone connected to this crime is placing the public in imminent danger.”

At least 49 people were killed and 53 injured in the attack, which was the worst mass shooting in US history and the deadliest terror attack on American soil since 9/11.

Police described Mateen as “cool and calm” as he phoned emergency services from a bathroom where he was holding hostages, pledging allegiance to Isis leader Abu Bakr al-Baghdadi and expressing support for other terrorists.

The 29-year-old was shot dead in a gun battle with police who stormed Pulse with armoured vehicles after a three-hour siege.

Isis claimed responsibility for the shooting, calling the gunman “a soldier of the Caliphate”, but there was no indication that the terrorist group had contact with the gunman or directed the atrocity.

“It does appear that at the last minute he announced allegiance to Isil (Isis) but there is no evidence so far that he was in fact directed by Isil or that it was part of a larger plot,” Barack Obama said.

It appeared that Mateen had been radicalised online, the President said, calling him “an example of home-grown extremism”.

The FBI's had investigated Mateen for 10 months and interviewed him twice after colleagues raised concerns over radicalisation in 2013 but found no evidence of a crime or connection with a militant group.

There have been conflicting reports of motivation for his attack, with his former wife saying he was mentally ill and his father telling media he had been angered by seeing two men kiss, while acquaintances claim Mateen was himself gay but felt unable to be open about his sexuality.