In the wake of a series of fatal terrorist attacks in Brussels, Belgium, on Tuesday, Republican presidential front-runner Donald Trump said he would go beyond waterboarding when interrogating suspected terrorist leaders and repeated that the U.S. should "close up our borders until we figure out what's going on."

"Waterboarding would be fine and if they could expand the laws, I would do a lot more than waterboarding," Trump said Tuesday morning on NBC's Today, adding authorities should "should be able to do whatever they have to do." Asked if he believed people, when tortured, yield useful rather than false information, he said he was "in that camp."

"You have to get the information and you have to get it rapidly," he said.

On March 18, Belgian authorities captured Salah Abdeslam, whom they suspect of participating in the Nov. 13 terror attacks in Paris.

Trump's statements were quickly followed by comments from the other candidates. The Democratic front runner, Hillary Clinton slammed Trump's call to close the border as "unrealistic" and said torture was ineffective. On the Republican side, Texas Senator Ted Cruz called on President Obama to call the attacks an outgrowth of "radical Islam" while Ohio Gov. John Kasich urged a redoubling of efforts to root out the perpetrators of such acts.

"We can't be soft and weak," Trump said, suggesting the U.S. and Europe should observe laws around interrogation techniques but said "liberal" laws there have hampered terror investigations. The U.S. considers waterboarding torture.

Trump also repeated his earlier call to shutdown much immigration in the U.S., including almost all immigration by Muslims and refugees from Syria, and said poor assimilation by Muslims in Europe contributed to the attack.

"Assimilation is very, very difficult and in some cases impossible," Trump told Fox & Friends in an interview earlier Tuesday.

Trump said that Brussels, which is both the capital of Belgium and the European Union, "is an armed camp." He said he would not build ties between Muslim communities and the U.S. but rather said it was Muslims responsibility to bring concerns about possibile terrorist activities to the attention of authorities.

"They're very untrusting of people other than Muslims," he said. "Somehow that community doesn't believe in reporting."