Washington, Jun 16 (IANS): Omar Mateen, the gunman who killed nearly 49 people at a gay nightclub in Orlando, Florida, pledged allegiance to the Islamic State (IS) on Facebook message which he posted moments before the worst mass shooting in the US.

“America and Russia stop bombing the Islamic state..I pledge my alliance to (IS leader) Abu Bakr al Baghdadi ..may Allah accept me,” Mateen posted.

“The real muslims will never accept the filthy ways of the west” and “You kill innocent women and children by doing us airstrikes..now taste the Islamic state vengeance.”

According to the report, Mateen also declared allegiance to IS and al-Baghdadi in 911 calls he made during the attack, CBS News reported on Thursday.

A US Federal Bureau of Investigation (FBI) official said the massacre at the Pulse nightclub was both hate crime and an act of terror.

"This was an act of violence, born out of hate, that inflicted terror on an entire community," said Ron Hopper, special FBI agent in charge of the case.

"So I would call it a hate crime. I would call it terrorism. It's both," Xinhua news agency quoted Hopper as saying.

The US authorities were also considering filing criminal charges against Mateen's wife, Noor Salman, for failing to inform the FBI what she knew before the attack.

Salman, has told the FBI that she drove Mateen, 29, to the Pulse nightclub on a prior occasion but that she tried to talk him out of the deadliest mass shooting in modern US history, officials told NBC News.

Several officials familiar with what she has told the FBI said she was with him when he bought ammunition and a holster. She also once drove him to the nightclub because he wanted to see it in advance, the officials said.

The couple has been married since 2011. They have a three-year-old son.

The FBI is investigating reports that Mateen made several visits to the Pulse nightclub and made contact with other men on gay dating apps.

President Barack Obama was scheduled to travel to the scene of the attack in Orlando on Thursday.