ORLANDO — A source familiar with the investigation tells CBS News gunman Omar Mateen referenced the Islamic State of Iraq and Syria (ISIS) in a Facebook message posted moments before the Orlando nightclub shooting.

“You kill innocent women and children by doing us airstrikes..now taste the Islamic state vengeance [sic],” Mateen wrote, according to the source.

“In the next few days you will see attacks from the Islamic State [ISIS] in the usa,” the post said.

Mateen also declared allegiance to ISIS and leader Abu Bakr al-Baghdadi in 911 calls he made during the attack early Sunday morning, a U.S. intelligence source told CBS News.

ISIS claimed responsibility for the shooting on the group’s official radio station, al-Bayan.

“We begin from America, where Allah has enabled brother Omar Mateen, one of the soldiers of the Caliphate in America, to carry out a raid where he was able to infiltrate a Crusaders’ gathering at a gay night club in Orlando, Florida,” the radio report said.

“Allah enabled him to inflict heavy casualties amongst the filthy Crusaders,” the ISIS statement said. “He killed and injured over a hundred of them. This is the biggest raid to be carried in America after the raid of Manhattan 16 years ago. All praise to Allah.”

The FBI is characterizing the shooting at Pulse, a gay nightclub, as both a terrorist attack and a hate crime, CBS News’ Paula Reid reported.

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