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Donald Trump said Tuesday that authorities interrogating Paris terror suspect Salah Abdeslam should "do whatever they have to do" to get information in light of the deadly terrorist attacks in Belgium.

Trump said on NBC's "TODAY" if he were elected president he would make sure the United States has "strong borders," and said people looking to come into the country would need "absolute perfect documentation."

He and other presidential candidates reacted to the deadly explosions that rocked the main Brussels airport and the metro system near European Union buildings.

Brussels was on lockdown, with Tuesday's blasts coming four days after the arrest of Abdeslam.

A police woman gestures in front of ambulances at the scene of a blast outside a metro station in Brussels, in this still image taken from video on March 22, 2016.
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People gather around a memorial in Brussels following bomb attacks in Brussels, Belgium, March 22, 2016.
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Metro-North Railroad police officers patrol Grand Central Terminal, in New York, Tuesday, March 22, 2016.
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Abdeslam should be subjected to harsh interrogation techniques, Trump told NBC. Belgian authorities should be able to "do whatever they have to do" to get information from the suspect, he continued, adding waterboarding "would be fine."

"If they could expand the laws, I would do a lot more than waterboarding," he continued. "You have to get the information from these people. And we have to be smart. And we have to be tough. We can't be soft and weak."

Dismissing critics who say harsh interrogations don't yield reliable information, Trump said: "I am in the camp where you have to get the information, and you have to get it rapidly."

Trump made his first remarks on the Brussels terror attacks on Twitter.

"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!"

GOP rival Ohio Gov. John Kasich tweeted a statement on the Brussels attacks.

It read in part:

"We must ... redouble our efforts with our allies to identify, root out and destroy the perpetrators of such acts of evil," the Kasich statement read, in part. "We must strengthen our alliances as our way of life and the international system that has been built on our common values since the end of the Second World War comes under challenge."

It read, in part: "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," the Cruz statement continued, "we will name our enemy — radical Islamic terrorism. And we will defeat it."

Cruz later criticized Trump for saying to The Washington Post that he favors a light footprint in the world.

"Donald Trump is wrong that America should withdraw from the world and abandon our allies," Cruz told reporters Tuesday.

The Texas senator also called for a halt to the entrance of Syrian refugees into U.S. until a screening review can be conducted.

Democratic front-runner Hillary Clinton said in a statement Tuesday: "Terrorists have once again struck at the heart of Europe, but their campaign of hate and fear will not succeed."

The statement also read, in part: "Today's attacks will only strengthen our resolve to stand together as allies and defeat terrorism and radical jihadism around the world."

She also tweeted:

These terrorists seek to undermine the democratic values that are the foundation of our way of life. They will never succeed. -H

In an interview with MSNBC on Tuesday, Clinton outlined her strategy for stopping the spread of terrorism.

"I think we do have to have a clear objective of defeating ISIS, of defeating the tactics and activities of terrorists. That's something I've been talking about for some time," said Clinton. "I think the way to do that is to deprive them of territory in Syria and Iraq, to stop the flow of foreign fighters, arms, weapons, and to take them on the Internet, which they use in quite a sophisticated way. That means we have to work with other countries. We have to work with our European friends and allies."

Democratic candidate Vermont Sen. Bernie Sanders tweeted his reaction to the attacks.

We offer our deepest condolences to the families who lost loved ones in this barbaric attack and to the people of Brussels.

The Sanders statement also read, in part: "Today's attack is a brutal reminder that the international community must come together to destroy ISIS."

The Brussels attacks occurred ahead of Republican presidential nominating contests in Arizona, which is a winner-take-all, 58 delegate primary, and a 40-delegate caucus in Utah.

Democrats also hold an 85-delegate primary in Arizona and a 37-delegate caucus in Utah, in addition to a 27-delegate caucus in Idaho.

— CNBC's Krysia Lenzo contributed to this report.