Donald Trump took to Twitter Sunday to thank people for saying the Orlando attack showed he was "right" while warning that the tragedy is "just the beginning."

"Appreciate the congrats for being right on radical Islamic terrorism," he wrote. "I don't want congrats, I want toughness & vigilance. We must be smart!"

Read: Was Killed in 'Deadliest Shooting in American History' Inspired By Seeing Men Kiss?

It sparked a flurry of anger on the social network, with other users accusing the presidential hopeful of being tone deaf.

"Trump is a truly awful person," singer John Legend wrote as he quoted Trump's tweet.

"Once again, Donald, you have shown why you cannot lead us," George Takei wrote. "50 people are dead, and you bask in congratulations."

Senator John McCain's daughter, Meghan, asked: "You're congratulating yourself because 50 people are dead this morning in a horrific tragedy?"

At least 50 people were killed in the deadliest mass shooting in American history, and another 53 were injured, when suspected gunman Omar Mateen, 29, attacked Pulse in Orlando in the early hours of Sunday.

Mateen's father reportedly said his son recently became outraged after witnessing two men kissing. The suspected shooter, a U.S.-born citizen with Afghan parents, also pledged allegiance to ISIS in a 911 call during the attack, officials reportedly said.

Read: Orlando Suspect's Ex-Wife Says He Was Unstable

"At this time we're looking at all angles right now," an FBI official said at a press conference Sunday. "We do have suggestions that that individual may have leanings towards that, that particular ideology. But right now we can’t say definitively, so we’re still running everything around.”

In the aftermath of the shooting, Trump reiterated his call for a ban on Muslims entering the U.S.

"Reporting that Orlando killer shouted "Allah hu Akbar!" as he slaughtered clubgoers," he wrote.

He added: "What has happened in Orlando is just the beginning. Our leadership is weak and ineffective. I called it and asked for the ban. Must be tough."

Watch: Paul Ryan Calls Trump Comments 'Racist'