Trump called again for tougher US border security following Tuesday's attacks in Brussels, saying "we have to be very vigilant and careful about who we allow into our country."
As many as 34 people have been killed and more than 130 wounded in what is thought to be a pair of coordinated suicide attacks at Zaventem Airport and Maalbeek metro station in Brussels today.
"As president ... I would be very, very tough on the borders, and I would be not allowing certain people to come into this country without absolute perfect documentation," he told NBC.
"Well I'm not looking to break any news on your show, but frankly the waterboarding, if it was up to me, and if we changed the laws or have the laws, waterboarding would be fine," Trump said. "I would say they should be able to do whatever they have to do."
Trump also took to Twitter to say the US must be vigilant and smart.
Do you all remember how beautiful and safe a place Brussels was. Not anymore, it is from a different world! U.S. must be vigilant and smart!— Donald J. Trump (@realDonaldTrump) March 22, 2016
Trump's comments come after he previously said there should be a blanket ban on Muslims entering the US in the wake of the Paris terror attacks last November.
His rival Ted Cruz also took to Facebook to release at statement, which read: "Make no mistake — these terror attacks are no isolated incidents. They are just the latest in a string of coordinated attacks by radical Islamic terrorists perpetrated by those who are waging war against all who do not accept their extreme strain of Islam."
"When I am sworn in as president we will name our enemy — radical Islamic terrorism. And we will defeat it," he added.
On the Democrat side of the race Hillary Clinton said: "Terrorists have once again struck at the heart of Europe, but their campaign of hate and fear will not succeed."