(CN) - As the United States awoke to news that a series of deadly terrorist attacks had occurred in Brussels on Tuesday, the presidential candidates were already responding to the tragedy.
Appearing on Fox News Tuesday morning, Republican front-runner Donald Trump said "Brussels was a beautiful city ... now it's a disaster."
"I know Brussels well, and it is a total mess. It is a city that used to be one of the finest, one of the most beautiful and ... safest cities in the world. Now it's a catastrophic, dangerous city," he said, adding "We have to be very, very vigilant as to who we let into this country."
Trump reiterated his call for tightening controls at the U.S. borders, preventing refuges from Syria from entering the country, and waterboarding incarcerated terror suspects like Salah Abdeslam, who was arrested in Brussels earlier this week.
Belgian authorities should "do whatever they have to do" to get information on who carried out Tuesdays attacks, Trump said.
"I would do a lot more than waterboarding," he said. "We have to be smart. We have to be tough."
Trump made similar statements on NBC's "Today" show and during an interview with CBS News.
At least 36 died in the series of attacks, which included two explosions at the city's international airport and a third at a subway station in the heart of the city not far from the headquarters of the European Union.
The attacks come as voters in three states Arizona, Utah and Idaho prepare to head to the polls today to participate in primaries and caucuses.
Democrat Hillary Clinton said Tuesday morning that while terrorists "have one again struck at the heart of Europe ... their campaign of hate and fear will not succeed."
"The people of Brussels, of Europe, and of the world will not be intimidated by these vicious killers," Clinton said. "Today Americans stand in solidarity with our European allies. Our thoughts and prayers are with the families of those killed and wounded, and all the people of Belgium.
"These terrorists seek to undermine the democratic values that are the foundation of our alliance and our way of life, but they will never succeed. Today's attacks will only strengthen our resolve to stand together as allies and defeat terrorism and radical jihadism around the world," she said.
Meanwhile, her opponent in the race for the Democratic nomination, Sen. Bernie Sanders of Vermont, said "Today's attack is a brutal reminder that the international community must come together to destroy ISIS. This type of barbarism cannot be allowed to continue."
In a statement on his Facebook page, Sen. Ted Cruz of Texas said, "Our heart breaks for the men and women of Brussels this morning."
"Make no mistake, these terror attacks are not 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," Cruz said.
He continued: "Radical Islam is at war with us. For over seven years we have had a president who refuses to acknowledge this reality. ... That ends on January 20, 2017, when I am sworn in as president. We will name our enemy - radical Islamic terrorism. And we will defeat it."
Ohio Gov. John Kasich also released a statement, expressing his "solidarity" with the people of Belgium in the wake of the attacks.
"Along with every American, I am sickened by the pictures of the carnage, by the injuries and by the loss of life," Kasich said.
"The wave of terror that has been unleashed in Europe and elsewhere around the world are attacks against our very way of life and against the democratic values upon which our political systems have been built," he continued. "We and our allies must rededicate ourselves to these values of freedom and human rights. We must utterly reject the use of deadly acts of terror."
Kasich added: "We must also redouble our efforts with our allies to identify, root out and destroy the perpetrators of such acts of evil. 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 from these and other actors of evil."
Read the Top 8
Sign up for the Top 8, a roundup of the day's top stories delivered directly to your inbox Monday through Friday.