Trump thanks supporters for praise about 'being right' after Orlando shooting
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Presumptive GOP presidential nominee Donald TrumpDonald John TrumpOn North Korea, give Trump some credit Exclusive: Bannon says Rosenstein could be fired 'very shortly' GOP dissidents on cusp of forcing immigration votes MORE on Sunday thanked his supporters for their praise after an attack at an Orlando, Fla., nightclub that left 50 people dead and many more injured.

"Appreciate the congrats for being right on radical Islamic terrorism, I don't want congrats, I want toughness & vigilance," Trump tweeted Sunday.

"We must be smart!"

The tweet sparked a backlash over its content and timing.

The attack at the Orlando nightclub early Sunday morning is considered the worst mass shooting incident in U.S. history.

It took place at a gay club during Pride Month.

Police said the shooter, who was killed inside the nightclub during a shootout with police, had an assault-style rifle, a handgun and "some type of device."

An agent from the FBI's Orlando field office said there are "suggestions" the suspect may have had "leanings" toward radical Islamic ideology. But it was not immediately clear if the incident was inspired by foreign terrorism.

Rep. Adam SchiffAdam Bennett SchiffConservatives leery of FBI deal on informant No Dems invited to attend meeting on Russia docs Trump officials brief Congress on election cyber threats behind closed doors MORE (D-Calif.) said he was told the shooting suspect had pledged allegiance to the Islamic State in Iraq and Syria. 

Trump tweeted about the attack earlier in the day, calling it a "horrific incident" and calling for the country to get "tough, smart & vigilant."

As of Sunday, Trump had not changed his schedule for the upcoming week. He is scheduled to give a hard-hitting speech Monday on the Clintons.

— This report was updated at 1:30 p.m.