Orlando nightclub shooting is the deadliest in US history

AP Photo/Phelan M. Ebenhack

Police officers stand guard down the street from the scene of a shooting involving multiple fatalities at a nightclub in Orlando, Fla., Sunday, June 12, 2016.

The mass shooting at an Orlando, Florida, nightclub early Sunday morning is the deadliest in US history.

At least 50 people were confirmed dead and 53 more injured after a gunman, reported as Omar Mateen, opened fire and barricaded himself inside a gay nightclub Sunday morning in what is now being investigated as an act of terrorism.

The FBI special agent in charge said there were indications that Mateen subscribed to a radical Islamic ideology, and Rep. Adam Schiff - a top Democrat on the House Intelligence committee - said that Mateen had pledged allegiance to ISIS.

The shooting had more fatalities than either the Virginia Tech shooting in 2007 (32 dead) and the mass shooting at Sandy Hook Elementary School in Newtown, Connecticut in 2012 (27 dead).

It's the deadliest incident on US soil since the September 11, 2001, terrorist attacks, according to Rep. Michael McCaul, the chair of the House Homeland Security Committee.

Connecticut Sen. Chris Murphy, who was a congressman serving the district encompassing Newtown in 2012, said Congress "has become complicit in these murders."

"I'm aching for the victims, their loved ones, and the people of Orlando, and I pray that all those injured have a quick and full recovery," the Democrat wrote in a statement. "I know the pain and sadness that has brought too many communities - Newtown, Oregon, Aurora, San Bernardino, and now Orlando - to their knees, and I can only hope that America's leaders will do something to prevent another community from being added to the list."

"This phenomenon of near constant mass shootings happens only in America - nowhere else," Murphy continued. "Congress has become complicit in these murders by its total, unconscionable deafening silence. This doesn't have to happen, but this epidemic will continue without end if Congress continues to sit on its hands and do nothing - again."

Wisconsin Sen. Ron Johnson, chair of the Senate Homeland Security and Governmental Affairs Committee, called on Americans to "unite to defeat terrorism's threat to our nation's society."

"My thoughts and prayers are with the victims and their families and the brave men and women who risked their lives to save others," the Republican senator wrote. "My committee will work to support the federal role in investigating this terror attack and protecting against further threats. As Americans we must unite to defeat terrorism's threat to our nation's security."

Natasha Bertrand contributed to this report.