The Islamic State in Iraq and Syria (ISIS) claimed responsibility Sunday for a deadly nightclub shooting in Orlando, Fla., that left 50 dead and 53 injured.

"The attack that targeted a nightclub for homosexuals in Orlando, Florida and that left more than 100 dead and wounded was carried out by an Islamic State fighter," ISIS said in a statement.

ADVERTISEMENT

The organization offered no proof for the attacks.

ISIS takes responsibility for #OrlandoShooting through the Amaq Agency. pic.twitter.com/F39SqBbMtM — Sheera Frenkel (@sheeraf) June 12, 2016

Florida Sen. Marco Rubio Marco Antonio RubioSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Florida senators pushing to keep Daylight Savings Time during pandemic Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll MORE (R) also referenced the United States’s ongoing fight against terrorism but said the FBI would have more information about possible connections to terrorism.

Fifty people were killed and 53 others were injured early Sunday morning when a gunman opened fire inside the Pulse nightclub in the deadliest mass shooting in U.S. history.

Federal law enforcement officials say the gunman was Omar Mateen, a 29-year-old American citizen living in Port St. Lucie, Fla. He was killed at the scene in a shootout with police.

He was reportedly armed with an AR-15-style assault rifle and a handgun.

News networks reported Mateen phoned 911 moments before the shooting to pledge allegiance to ISIS.

It remains unclear if the planning and execution of the attack were directly linked to foreign terrorist groups.

President Obama Sunday called the shooting an "act of terror" but didn't place blame on the terror group.