Donald Trump tweets that he was 'right' about terrorism after Orlando mass shooting

Donald Trump's tweet after more than 50 people died in what's being called the worst mass shooting in U.S. history. Donald Trump's tweet after more than 50 people died in what's being called the worst mass shooting in U.S. history. Image 1 of / 20 Caption Close Donald Trump tweets that he was 'right' about terrorism after Orlando mass shooting 1 / 20 Back to Gallery

Hours after a mass shooting being investigated as an act terrorism left 50 people dead in Florida, Republican presidential candidate Donald Trump tweeted that he was "right" about radical Islamic terrorism.

It was unclear whether the shooter who killed at least 50 people in an Orlando, Florida nightclub was associated with a radical religious organization. President Barack Obama addressed the nation, calling the shooting "an act of terror" and an "act of hate."

Trump tweeted as Obama began speaking: "Is President Obama going to finally mention the words radical Islamic terrorism? If he doesn't he should immediately resign in disgrace!"

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The shooter in what has been called the worst mass shooting in U.S. history was identified Sunday as Omar Mateen. According to reports, Mateen had pledged allegiance to ISIS and has been on the "radar" of U.S. agencies. As of 12:35 p.m., there was no indication of the Islamic extremist group's direct involvement in the deaths.

Trump, who has called for a ban on all Muslim immigration to the United States, implied we was being congratulated for his hard line in the sand.

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

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Some criticized the tweet for being insensitive and inappropriate given the day's events.

"You're the only person in America who would or could 'appreciate the congrats' while families mourn 50 dead," Chris Sacca from NBC's "Shark Tank" tweeted.

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The tweet came after another tweet an hour earlier that shared his condolences for the families who lost loved ones.

"Horrific incident in FL. Praying for all the victims & their families. When will this stop? When will get tough, smart & vigilant?"

>> Click the gallery above to see some of Trump's most controversial campaign moments.

The Associated Press contributed to this report