In the wake of the deadliest shooting in U.S. history, likely Republican presidential nominee Donald Trump said he was "right on radical Islamic terrorism" and called for toughness and vigilance.

Trump made the statement on Twitter after the attack in an Orlando, Florida nightclub which 50 killed people and wounded 53.

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

The Orlando shooter, who was killed by police, was identified as a Florida resident, Omar S. Mateen.

An FBI official said Mateen might have leanings toward Islamic State's ideology but cautioned that the suspected Islamist connection required further investigation.

Trump has proposed a temporary ban on Muslim immigration to the United States as a way to combat the threat of radical Islamist attacks.

Hillary Clinton, the presumptive Democratic nominee, tweeted a brief statement after the attacks, but did not speculate on the motives of the gunman.

"Woke up to hear the devastating news from (Florida). As we wait for more information, my thoughts are with those affected by this horrific act," Clinton wrote.

Trump had earlier tweeted that he was praying for the victims and their families.

(Reporting by James Oliphant; Editing by Meredith Mazzilli and Alistair Bell)