At a campaign rally in Ohio, he said in regard to the torture method: 'I like it a lot. I don't think it's tough enough'
Presumptive Republican presidential nominee Donald Trump advocated for the use of waterboarding against Islamic State (IS) group militants on Wednesday.
In regards to the controversial practice, he said: "I like it a lot."
He reiterated his support for waterboarding mere hours after three suicide bombers attacked Istanbul’s Ataturk airport that killed 41 people and wounded 200 more. Turkish authorities believe IS was likely responsible for the attacks.
Trump said, "You have to fight fire with fire," after making a note about IS beheadings.
"We have to fight so viciously and violently because we're dealing with violent people," he added.
US President Barack Obama has called waterboarding torture and the method was banned under George W Bush’s presidency in 2006.
Waterboarding is the act of placing a cloth over a captive’s face and pouring water down the person's throat to stimulate drowning. It can cause severe damage to the lungs and brain as well as death.
John McCain, a Republican US senator from Arizona, strongly disagreed with Trump’s comments.
"It's not the United States of America. It's not what we are all about. It's not what we are," said McCain, who was a prisoner of war during the Vietnam War and tortured by the Vietcong.
Trump and his Democratic rival for president, former secretary of state Hillary Clinton, have both seen a decrease of support, a poll released on Wednesday showed.
Respondents to the latest Quinnipiac University national poll put Clinton ahead of Trump just 42 percent to 40 percent, a narrowing from Clinton's four-point margin in the organisation's 1 June survey.
It is also considerably closer than the 12-point Clinton advantage in an ABC News/Washington Post poll published Sunday which highlighted Clinton capitalising on Trump's recent missteps.
During Trump’s rally, the real estate mogul asked the crowd: “What do you think about waterboarding?"
As the crowd cheered, Trump said, "I don't think it's tough enough."
It was not the first time Trump has shown support for the practice. During a Republican primary debate in February he vowed to "bring back a hell of a lot worse than waterboarding".