2016 Candidates Express Solidarity With Brussels

— -- U.S. presidential candidates are expressing support for the people of Brussels and suggesting U.S. responses to the deadly terror attacks in Belgium's capital.

Dozens have been confirmed dead in multiple explosions in Brussels, with at least three Americans "seriously injured." Blasts were reported at the international airport and a subway station near a European Union office.

Here's what the 2016 contenders had to say about the tragic events:

Donald Trump

Trump appeared on "Good Morning America" today and called the attacks "horrible."

"I was in Brussels many times over the years. And it used to be a safe and beautiful city. And then it really changed," Trump told ABC News' George Stephanopoulos. "And I want to tell you, now it's like an armed camp. Anybody that goes there will tell you it's like an armed camp. I'm talking about before this morning's brutal attack. It was a horrible attack. And Brussels is different and Paris is different and lots of places are different. And the police don't have control of it anymore. And it's a very sad thing to see what's happening."

Donald Trump also tweeted this morning, "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!”

Trump also repeated his calls for surveillance of mosques in the wake of the terror attacks.

"You need surveillance and deal with the mosques," Trump told Fox Business. "These attacks aren't done by Swedish people, that I can tell you. Look, we have to be smart, we have to be vigilant. We have to watch closely what's going on. We have to look at the mosques and study what's going on."

Hillary Clinton

Democratic front-runner Hillary Clinton also appeared on "Good Morning America" this morning, calling the attacks "an act of coordinated terrorism" and telling Stephanopoulos that “we’ve got to strengthen our resolve to stand together within our own country rather than dividing our own country."

“I think we have to intensify and broaden our strategy," Clinton said, adding that the United States, Europe and NATO need to “intensify” their cooperation.

She rebutted Trump’s call for waterboarding and torture tactics. “That is just another one of his claims that doesn't bear up. Our best and bravest military Intel leaders will tell you torture is not effective,” she said.

And she said that tightening our borders to prevent Muslims from entering the country, as Trump proposes, “shows a lack of understanding of how our system does work.”

Ted Cruz

At a news conference on Capitol Hill today, Sen. Ted Cruz, R-Texas, called on President Obama to ditch his visit to Cuba and either travel home or to Brussels.

“While our friends and allies are attacked by radical Islamic terrorists. President Obama is spending his time going to baseball game with the Castros and standing at a press conference with Raul Castro as a prop while Castro denies there are any political prisoners in Cuba,” Cruz said.

Cruz also argued: “Today's attacks in Brussels underscores that this is a war. This is not an isolated incident. This is not a lone wolf. This is a war with radical Islamic terrorism.”

A later Cruz statement called for a stop to refugees from countries where terrorist organizations have a significant presence.

"We need to immediately halt the flow of refugees from countries with a significant al Qaida or ISIS presence," he said. "We need to empower law enforcement to patrol and secure Muslim neighborhoods before they become radicalized."

John Kasich

In a statement released today, Ohio Gov. John Kasich wrote that he wants to "express my solidarity with the people of Belgium" and that he is "sickened by the pictures of the carnage, by the injuries and by the loss of life."

Kasich reiterated his fellow GOP contender Cruz's calls for President Obama to return home from Cuba.

"First of all I’m a little surprised that the president is going to a baseball game when I believe he should, had I been president I would have cut short my visit," Kasich told reporters in Minneapolis, Minnesota. "I would’ve flown home, I would’ve conducted calls jointly with heads of state and gone to assemble teams of people, intelligence experts, who can take a look at the serious breaches that we have in intelligence."

Kasich also added: "I believe the president should return to Washington, we have a major international terror situation and I think to be not in the country rallying support behind our friends in Europe is a mistake."

But he diverges from the other two GOP candidates on whether the U.S. should monitor Muslim communities. "Just because you happen to be a Muslim doesn’t mean that you are a radicalized person that wants to destroy somebody in the West," Kasich argued, adding later, "This is a time where you have to remain strong but not a time in which you should let your rhetoric take advantage of a situation where people may be frightened."

Bernie Sanders

Democratic presidential candidate Bernie Sanders tweeted late this morning about the Brussels attacks.

"Today's attack is a brutal reminder that the international community must come together to destroy ISIS," Sanders said in a statement. "This type of barbarism cannot be allowed to continue.”

At a news conference in Flagstaff, Arizona, today, the Vermont senator advocated for a coalition of the Muslim countries in the region, with support from the United States and its allies to defeat ISIS. Sanders also said there needs to be "improved intelligence sharing" between the United States and its allies and "effective monitoring of social media to stop the recruiting efforts of young people who are being led to the terrible life of terrorism."

Sanders said he "strongly disagrees" with Trump and Cruz's push to monitor Muslim mosques and communities.

"That would be unconstitutional; it would be wrong,” Sanders said. "We are fighting a terrorist organization, a barbaric organization that is killing innocent people. We are not fighting a religion."

ABC News' Alana Abramson, Lissette Rodriguez, Ben Gittleson and John Santucci contributed to this report.