Orlando gay club massacre: Cops poised to swoop on gunman accomplice suspect

US authorities say they are about to close in on a suspect linked to the man who murdered 49 people in a crowded Florida nightclub.

By Patrick Knox

MYSTERY: It is thought the killer had an accomplice

It was thought Omar Mateen was a lone wolf attacker inspired by ISIS when he slaughtered revellers at Orlando gay club Pulse in the early hours of Sunday morning. 

But now detectives and the FBI believes he may have conspired to kill with someone else.

A top law enforcement source told WFTV-TV that the suspected accomplice would be arrested within hours but authorities did not release any additional details.

The suspected accomplice is either in Florida or has ties to the state, the TV station reported.

EVIL: Mateen may not have been a lone wolf

Mateen, 29, was killed in a shootout with police during the deadly rampage.

Meanwhile US Homeland Security Secretary Jeh Johnson called on Tuesday for "meaningful, responsible" gun control measures following the Florida nightclub massacre, saying steps were needed to keep firearms out of the hands of people who might be planning terrorist attacks.

Johnson, in several morning television interviews, said such curbs were a critical step for public safety and could be taken without infringing on the rights and abilities for responsible people to own a gun.

"This has become a matter of homeland security," Johnson told CBS News.

"We need to do something.

"We need to minimize the opportunities for terrorists to get a gun in this country."

ISIS have since claimed responsibility for the massacre and warned that Mateen was just one of many in the American cell operating under their directions.

But the gunman's dad Seddique Mateen said religion had "nothing to do with" it and even blamed lax nightclub security for the atrocity.

It also emerged today that gunman may have been gay, using the dating app Jack'd and being a regular at the nightclub.