Orlando gunman Omar Mateen identified himself as an Islamic soldier in calls with authorities during his rampage and demanded to a crisis negotiator that the US "stop bombing Syria and Iraq", according to transcripts released by the FBI on Monday.

The partial transcripts were of a 911 call made by Mateen and three conversations he had with the police crisis negotiators during the worst mass shooting in modern US history, in which 49 people died and dozens were wounded.

Those communications, along with Facebook posts and searches Mateen made around the time of the shootings, add to the public understanding of the final hours of Mateen's life and to the possible motivations behind the rampage.

The first call came more than a half-hour after shots rang out, when Mateen told a 911 operator, "Praise be to God, and prayers as well as peace be upon the prophet of God," he told the dispatcher, referring to God in Arabic.

"I let you know, I'm in Orlando and I did the shootings."

During the 50-second call with a dispatcher, Mateen made murderous statements in a "chilling, calm and deliberate manner", Ronald Hopper, FBI assistant special agent in charge in Orlando, said during a news conference.

However, there is no evidence Mateen was directed by a foreign terrorist group, and he was radicalized domestically and on his own, Hopper said.

Mateen's name and the groups and people to whom he pledged allegiance were initially omitted from the excerpt. But the Justice Department reversed course later Monday, providing a more complete transcript.