Republican presidential candidates seized on the terror bombings in Brussels Tuesday to demand that Muslim refugees be kept out of the United States, blaming Europe's open immigration policies for the outrage.
Frontrunner Donald Trump repeated his call for closing US borders "until we figure out what's going on" -- a call Democratic frontrunner Hillary Clinton said was unrealistic.
"Belgium is a horror show right now. Terrible things are happening. People are leaving. People are afraid. This all happened because, frankly, there's no assimilation," he said on NBC News.
Texas Senator Ted Cruz also called for suspending the resettlement of refugees from countries where the Islamic State group or Al-Qaeda control territory, saying the administration's plans to bring in tens of thousands of Syrians fleeing the civil war there "makes no sense."
"We need a president who unleashes the full force and fury on IS group and utterly destroys them. That the only way to keep us safe," he said, referring to IS group by an alternate acronym.
The apparently coordinated bomb blasts in Brussels -- for which the Islamic State group claimed responsibility -- ripped through the city's international airport and a metro train in a station, killing about 35 people.
The attacks came four days after Belgian authorities arrested Salah Abdeslam, the prime suspect in the November 2015 Paris attacks claimed by the IS group.
In the United States, the scenes from Brussels added fuel to an already inflamed Republican debate over immigration and the conduct of a US-led war against Islamic State fighters, who control large swathes of territory in Iraq and Syria.
"Belgium is no longer Belgium. Belgium is not the Belgium you and I knew from 20 years ago, which was one of the most beautiful and safest cities in the world," Trump told NBC.
Asked what he would say to the American people in the immediate aftermath of a terror attack, he added: "We are going to be very vigilant and tough. We're not going to allow it to happen to our country.
"If it happens, we'll find the people who did it and they'll suffer greatly."
Speaking to Fox News, Trump -- who has called for a ban on Muslims entering the United States -- described Brussels as once being "a beautiful city, a beautiful place with zero crime. And now it's a disaster city. It's a total disaster.
"We have to be very careful in the United States. We have to be very, very vigilant as to who we allow into this country."
Clinton -- who could possibly face Trump in November's general election -- countered that it was "unrealistic to say we're going to completely shut down our borders to everyone."
Ohio Governor John Kasich, the more moderate of the three remaining candidates in the Republican race, urged Obama to move quickly to examine US vulnerabilities and "dig in and begin to rebuild the intelligence we need worldwide."
"I think Europe popped up its doors without having a proper vetting process," he said, referring to the waves of immigrants from the Syrian civil war that have pushed into Europe.
He faulted Obama for not acting forcefully enough to bring down Syria's President Bashar al-Assad and for failing to establish no-fly zones.