An ISIS flag is seen in this picture illustration, Feb. 18, 2016. REUTERS/DADO RUVIC

A new propaganda video purportedly released by the Islamic State group, also known as ISIS, shows footage of the Sunday's attack on the Orlando gay nightclub where a gunman shot dead 49 people. According to media reports, the video has not been verified by authorities or the extremist group.

The video, which was released Tuesday, surfaced on ISIS channels with the title "Orlando Attack." The footage showed the image of Omar Mateen, the gunman who called 911 and pledged allegiance to ISIS just before attacking the Pulse nightclub in Orlando, Florida. The video also warned President Barack Obama about "bloodshed on your people" if U.S. forces, along with allies, continue to carry out airstrikes and attacks targeting the extremist group in Iraq and Syria.

Sunday's attack at nightclub is said to be the worst mass shooting in U.S. history. Mateen, reportedly a frequent visitor at the club, was killed during gun battle with law enforcement officials.

The White House and FBI said Monday that Mateen was a “homegrown extremist” who was “radicalized” through the internet. Obama told reporters in Washington, D.C., that the 29-year-old was “inspired by various extremist information that was disseminated over the internet.”