New footage has emerged showing the gunman who murdered 49 people in an Orlando nightclub in a mosque just days before the massacre.

Omar Mateen was seen on surveillance footage inside a mosque in Kissimmee, Florida, on June 8 - four days before he carried out the mass shooting at Pulse Nightclub in Orlando on June 12.

In the video, Mateen can be seen sitting in prayer before he gets up and walks out of the mosque.

Omar Mateen (pictured) was seen on security footage praying alone in a mosque for about 10 minutes just days before killing 49 people at Pulse Nightclub in Orlando

Omar Mateen (pictured) visited the American Muslim Leadership center in Kissimmee, Florida, on June 8

Imam Helmi Elagha, who released the footage from the American Muslim Leadership center, said he could not understand how Mateen could be praying while he was potentially thinking about the shooting.

'I'm just thinking, "How are you praying?... You were contemplating killing people in a couple of days",' Elagha said in a press conference, according to the Orlando Sentinel.

The imam went on to say Mateen was inside for about 10 minutes, and that it was not unusual for unknown people to visit the center as it is next to a highway.

'People will come here as travelers … and they'll pray and walk out,' he said.

Mateen was filmed as he got up from praying and walked past a group of men to leave the center

Imam Helmi Elagha, who released the footage from the American Muslim Leadership center, said his mosque is in no way associated with 'the terrorist' Mateen (pictured)

'The majority of the time, no interaction takes place.

'We're not associated with this terrorist. We're not associated with this murderer.'

Elagha added the center has been the subject of abuse since the shootings, with people making threatening phone calls and 'ranting' about ethnic cleansing on its Facebook page.

It comes after it was revealed Mateen blamed the shooting on a U.S. airstrike in May that killed an ISIS leader.

Phone conversations between the shooter and an FBI negotiator were released by a Florida court after a lawsuit filed by several news organizations.

The June 12 Pulse nightclub attack claimed 49 lives (pictured) and seriously injured 53 others

Mateen carried out the shooting at the Pulse nightclub (pictured) in Orlando on June 12, 2016

During the calls, Mateen blamed the attack on a bombing in May which killed Iraq's ISIS leader, Abu Wahib.

'That's what triggered it, OK?' Mateen told a police negotiator. 'They should have not bombed and killed Abu Wahid.' The transcript spelling of 'Wahid' is believed to be an alternative translation of the ISIS leader's name.

He also demanded the U.S. stop its air strikes, telling the Orlando police negotiator he had to, 'Tell America to stop bombing Syria and Iraq.

'They are killing a lot of innocent people,' Mateen, a New York-born son of an Afghan immigrant, said.