Three suicide bombers launched a 'major, co-ordinated' attack at Istanbul's Ataturk Airport killing 41 people and injuring 239.
The trio sprayed bullets into crowds of terrified passengers and security personnel before blowing themselves up.
Taking to Twitter following the horror, Trump said: "Yet another terrorist attack, this time in Turkey. Will the world ever realise what is going on? So sad."
And three hours later added: "We must do everything possible to keep this horrible terrorism outside the United States."
The Trump campaign later released a statement that said: "Our prayers are with the families of those killed and injured in Istanbul. The whole world is stunned and horrified."
It added: "We must take steps now to protect America from terrorists, and do everything in our power to improve our security to keep America safe."
The billionaire businessman told a rally in St Clairsville, Ohio, that "there's something going on that's really, really bad. We better get smart and we better get tough or we're not going to have much of a country left".
At the same event, he reiterated his call for the return of waterboarding and the use of other harsh interrogation techniques in the battle against Isis (Islamic State) militants.
At one point, he asked the crowd: "What do you think about waterboarding?"
They cheered as he said: "I like it a lot. I don't think it's tough enough".
Waterboarding, described by US President Barack Obama as torture, was banned by the US in 2006.
During the Republican primary, Trump frequently advocated the return of waterboarding and "much worse," declaring at one point that "torture works".
He told the Ohio crowd: "We have to fight so viciously and violently because we're dealing with violent people."
Trump is continuing his harsh rhetoric as he approaches the general election campaign, even as his advisers work to make him more measured.
Hillary Clinton said the bombings at Istanbul Ataturk Airport are "a reminder that the United States cannot retreat".
The presumptive Democratic presidential nominee says that the US must deepen its cooperation with allies and partners in the Middle East and Europe "to take on this threat".
Clinton says: "Such cooperation is essential to protecting the homeland and keeping our country safe."
