Orlando gunman Omar Mateen had 'strong indications of radicalisation'

The gunman in the Orlando nightclub attack that killed 49 people had "strong indications of radicalisation" and was likely inspired by foreign terrorist organisations, the head of the FBI has said.

Director James Comey told reporters that Omar Mateen spoke with a 911 operator three times early on Sunday morning.

Mateen also pledged loyalty to the head of the Islamic State group on his last call, Mr Comey added.

The FBI investigated Mateen for 10 months beginning in May 2013. Mr Comey said investigators later introduced him to confidential sources, followed him and reviewed details of some of his communications.

The early Sunday attack marked the deadliest mass shooting in modern US history. Mateen died in a gun battle with police.

Meanwhile, President Barack Obama said there was no clear evidence that Mateen was directed to conduct his attack or part of a larger plot.

He said it appears Mateen was inspired by extremist information disseminated over the internet.

President Obama said the investigation is at the preliminary stages and is being treated as a terrorism investigation.

He said the attack appears to be similar to last year's shooting spree in San Bernardino, California.

The added investigators were still looking into the motivations of the shooter, including the fact that the shooting took place at a gay venue.

President Obama spoke in the Oval Office after being briefed on the investigation by FBI Director James Comey, Homeland Security Secretary Jeh Johnson and other officials.