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The Islamic state known as ISIS has claimed responsibility for the deadly attacks early Sunday morning in Orlando, Florida, that left 50 dead and 53 injured.

The report comes from ISIS-affiliated news outlet Amaq Agency.

The lone assailant, a 29-year-old American-born man named Omar Mateen, called 911 during the Orlando attacks, pledging his allegiance to ISIS, officials said.

Also Read: President Obama Denounces Orlando Massacre as 'Act of Terror,' 'Act of Hate'

“The armed attack that targeted a gay night club in the city of Orlando in the American state of Florida which left over 100 people dead or injured was carried out by an Islamic State fighter,” Amaq said, according to Reuters.

While at the scene, Mateen also mentioned the Tsarnaev brothers, who carried out the deadly 2013 bombings at the Boston Marathon.

It is unclear if Mateen had been in contact with any individuals from the Islamic State or was acting as a lone wolf in support of the group’s radical ideology.

Also Read: Presidential Candidates, Hollywood 'Devastated' by Orlando Nightclub Mass Shooting

The Orlando massacre is considered the worst mass shooting in U.S. history and the biggest terror attack since the tragic events on Sept. 11, 2001.

Mateen was born in New York City to Afghan parents, according to NBC News. He worked as a private security guard and lived in Port St. Lucie, Florida, which lies 125 miles south of Orlando where the massacre takes place.

Mass Shootings in America That Horrified All of Us (Photos)

Newtown, Conn. - On December 14, 2012, 20-year-old Adam Lanza fatally shot 20 children at Sandy Hook Elementary School. They were between the ages of six and seven years old. He also killed six adult staff members.
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Washington D.C. — A former Navy reservist shot and killed 12 people on September 16, 2013, at a military facility. The gunman was killed.
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Tyrone, Mo. - On Feb. 27, 2015, Joseph Jesse Aldridge killed seven people — four of them relatives — in a door-to-door shooting spree before killing himself.
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Waco, Tex. - Nine people were killed and many more were injured after two biker gangs began firing at each other at a motorcycle club on May 17, 2015.
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Charleston, S.C. - Dylann Roof shot and killed nine people during a racially motivated shooting in a predominantly African-American church on June 17, 2015.
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Chattanooga, Tenn. - A gunman named Mohammod Youssuf Abdulazeez entered two military facilities on July 16, 2015, and killed four Marines and injured others, before he was killed.
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Umpqua, Ore. - On October 1, 2015, Chris Harper Mercer killed nine people and injured seven to nine more at Umpqua Community College before two police officers shot him. Mercer then committed suicide.
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San Bernardino, Calif. - 14 people were killed and another 21 injured after Syed Farook and Tashfeen Malik opened fire during a holiday party on December 2, 2015. The pair were later killed during a shootout with police.
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Orlando, Fla. - 50 people were killed and 53 wounded on June 11, 2016, at Pulse, a gay nightclub. Just before the shooting, suspected killer Omar Mateen called 911 and pledged his allegiance to the terror group ISIS. Mateen was also shot an killed by police on the scene.
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TheWrap looks back at recent mass shootings that have happened on U.S. soil

Newtown, Conn. - On December 14, 2012, 20-year-old Adam Lanza fatally shot 20 children at Sandy Hook Elementary School. They were between the ages of six and seven years old. He also killed six adult staff members.

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