Donald Trump has been criticised for his lack of empathy after saying he appreciated being congratulated "for being right" in the wake of the most deadly mass shooting incident in US history.
The suspected shooter, Omar Mateen, 29, called 911 to pledge allegiance to the Islamic State before opening fire at Pulse, a popular gay nightclub in the Florida city of Orlando.
The Islamic State has claimed responsibility for the attack, which left 50 people dead, and a further 53 people injured.
"The armed attack that targeted a gay night club in the city of Orlando in the American state of Florida which left over 100 people dead or injured was carried out by an Islamic State fighter," Islamic State's Amaq news agency said.
Following the mass shooting, Trump took to Twitter to share his concern for the families of the victims.
But the presumptive Republican presidential nominee quickly switched to campaign mode, seemingly using the horrific attack as an opportunity to drive home his message.
He then went on to criticise Barack Obama's leadership, and to claim he had "called it".
Trump has previously proposed a temporary ban on Muslim immigration to the United States as a way to combat the threat of radical Islamist attacks.
President Barack Obama has since said the FBI was investigating the shooting as an act of terrorism, an announcement he made about 12 hours after the gunfire began at Pulse.
"We know enough to say that this was an act of terror and an act of hate," Obama said.
Meanwhile, the presumptive Democratic nominee, Hillary Clinton, was said to be "more empathetic" when she took to Twitter overnight to say she had woken up to hear the "devastating news", adding that her "thoughts are with those affected by this horrific act".
British Labour MP Ed Miliband commented on the difference in the tweets from Trump and Hilary Clinton.
"The difference in tone is striking. Clinton was empathetic and sorrowful. Trump was triumphant and aggressive," he tweeted.
The Washington Post wrote that Trump's tweet "speaks to the single largest problem facing his presidential campaign".
"While he's mastered the role of tough and unapologetic leader, he simply cannot seem to understand that at times a president needs to be an empathetic consoler in chief, too."
The article continued: "Trump's tweet feels decidedly off in the context of the tragedy playing out in Orlando. That people are congratulating him about being right about the threat posed by the Islamic States feels like the sort of thing that could have certainly waited a few days - or forever - to publicize. Making a moment like this one about yourself - "I was right!" is the essence of Trump's tweet - is a giant swing and miss when it comes to understanding what the broader nation requires of its leaders."
Several people have taken to Twitter to express their anger over Trump's tweets.
The gunman was shot dead and police say they are not looking a second suspect.
The FBI says Mateen had twice been investigated by the bureau and that in both cases the probes were "inconclusive" so there was nothing to keep the investigations going.
An FBI official said Mateen might have leanings toward Islamic State's ideology but cautioned that the suspected Islamist connection required further investigation.