CUBA -- President Barack Obama pledged to stand in solidarity with Belgium in condemning Tuesday's terror attacks that killed dozens in Brussels.
The three explosions killed at least 34 people and wounded about 170 more, according to Belgian media, and raised the reality of terror once again in the heart of Europe.
"The thoughts and prayers of the American people are with Belgium after the attacks in Brussels, and the United States stands in solidarity with Belgium in condemning the attacks," Obama said during a speech in Havana, Cuba.
"We can and we will" defeat terrorists, he said. "This is yet another reminder that the world must unite," he added. "We must be together, regardless of" nationality or faith or race, in fighting terrorism, he said.
Belgian federal Prosecutor Frederic Van Leeuw said late Tuesday morning that it was too soon to know exactly how many people died in the bombings. Yet Belgian state broadcaster RTBF, citing emergency services, reported 20 dead at the Maalbeek metro station and 14 more killed at Brussels' international airport.
"We were fearing terrorist attacks, and that has now happened," Belgian Prime Minister Charles Michel told reporters.
After the blasts, Belgian authorities again hit the streets looking for those tied to Tuesday's carnage and who might launch more attacks.
Citing judicial sources, RTBF reported that raids were underway midday Tuesday around Brussels, targeting people linked to the attacks. And at the international airport, a controlled explosion could be heard after troops zeroed in on a suspicious package, according to the Belgian crisis center.
While there's been no official claim of responsibility, many prominent ISIS supporters celebrated Tuesday's deadly terror attacks in Brussels on social media.
One widely circulated Twitter post among these ISIS backers featured the words, "What will be coming is worse."
Belgium is no stranger to terror. Just a few days ago, authorities there captured Europe's most wanted man, Salah Abdeslam -- the latest of many suspected terrorists caught in the small European country. And a U.S. counterterrorism official said, "The Belgians have been sitting on a ticking time bomb," given all those who have gone to Syria and Iraq to join ISIS, then possibly come back home.
Still, these facts don't take away the shock and horror of those who lived through Tuesday's carnage.
"You cannot believe it; you cannot believe it," said Jef Versele, who was in the airport's departure hall when bombs exploded there. "It was so insane. Not in my backyard."
Brussels man: 'It was a matter of time'
At least one of the two airport explosions was a suicide bombing, Van Leeuw said. A blast happened there outside the security checkpoints for ticketed passengers and near the airline check-in counters, an airline official briefed on the situation said.
The subway station blast happened in the Brussels district of Maalbeek, near the European Quarter, where much of the European Union is based.
Richard Medic, who arrived at the station shortly after that explosion, wasn't surprised by the carnage after all that Europe has gone through recently, including November's massacre in Paris that ISIS claimed responsibility for.
"I think, after the Paris attacks, we were assuming something like this would happen," the Brussels resident told CNN. "And it was a matter of time."
Yet Versele, the airport witness, said that he thinks Belgians should not hole themselves up.
Instead, he said, they should continue to live their lives and travel "to prove that we're not afraid of those who have done (the attacks)."
Europe, U.S. on alert as well
Belgian authorities bolstered security after Tuesday's attacks, including shutting down all Brussels metro stations and evacuating the city's airport.
This comes as the terror threat level in Belgium went up to four -- its highest. That step-up means that army soldiers can be sent onto the streets to meet security needs.
In addition to the airport, broadcaster RTBF reported that the National Pensions Office in Brussels had been cleared after two suspicious packages were found inside.
All but essential staff were also sent home from a nuclear power plant in the eastern city of Tihange, said a representative of Engie, the French company that operates the facility. Belgian authorities ordered this evacuation, though the representative did not provide further details.
The effects of Tuesday's attacks have been felt outside the Belgian capital as well.
As far away as the United States, authorities in places like New York, Washington, Chicago and Los Angeles took special precautions like increased K9 sweeps of subways and additional police patrols. This was especially true around airports, subway stops and train stations, with scenes like those in the U.S. capital -- where police pulled out and checked travelers at random -- not uncommon.
Similar, if not more intense measures were enacted around Europe.
NATO, the military alliance that is headquartered in Brussels, increased its own alert level and expressed solidarity with Belgium.
"This is a cowardly attack, an attack on our values and on our open societies," NATO Secretary General Jens Stoltenberg said in a statement. "Terrorism will not defeat democracy and take away our freedoms."
European calls for solidarity
As in other places, British authorities ordered an increased police presence at ports, airports, Tube stations and international train stations, said Prime Minister David Cameron.
Eurostar, a high-speed railway that goes to England and France, noted a number of schedule and other changes, including canceling service between London and Brussels.
Gare du Nord station in Paris, a stop for Eurostar as well as subway trains, was evacuated Tuesday afternoon after an abandoned suitcase was found, police said. Throughout France, 1,600 more police hit the streets after the Brussels attacks, French Interior Minister Bernard Cazeneuve said.
"I express my entire solidarity with the Belgian people," French President Francois Hollande tweeted. "Through the Brussels attacks, the whole of Europe has been hit."
That sentiment was echoed by Belgium's Michel during what he called "a dark time for our country."
"More than ever, I call on everybody to show calm, but also solidarity," the Prime Minister said. "We are facing a difficult, challenging time. And we should face up to this challenge by being united."
Airport witness: Windows broken, ceiling parts down
The darkness set in not long after the sun rose in Brussels. Anthony Barrett said he heard something about 8 a.m. local time from his hotel across from the terminal building.
"When I opened the curtains and looked out, I could see people fleeing," he told CNN.
Barrett saw stretcher after stretcher carrying people out of the airport, with luggage trollies also used to transport the wounded.
In the airport's departure hall, witness Versele noticed "people ... shouting and running around" after the first blast, then even more pandemonium after the second explosion, which was, "in my eyes, much more powerful."
That blast blew out windows, created a lot of smoke and caused parts of the ceiling to fall, he added.
"People were on the floor," Versele said, estimating that he saw 50 to 60 people who seemed to be unable to walk. "... It was quite a mess."
Traveler Jeffrey Edison had cleared security and was out by the gate, several hundred yards from the departure lounge, where the explosions occurred. He told CNN he didn't hear the blasts but "suddenly saw" 200 to 300 people rushing toward him from the security checkpoint.
He says it took authorities around 25 minutes to tell the passengers what had happened, before evacuating the area and leading the passengers to the runways.
Officials have not yet named those killed or wounded. The injured at the airport do include three Mormon missionaries -- ages 19, 20 and 66 -- from Utah, according to the Church of Jesus Christ of Latter-day Saints.
Soccer star: 'I wish for Brussels to act with dignity'
About an hour later, during the tail end of Brussels' rush hour, another blast went off at the Maalbeek metro station.
Sander Verniers was heading toward there when this explosion occurred, producing "strong winds going (through his train) and some noises that shouldn't be there." Belgian troops met the passengers as they got off the train and walked along the tracks.
"We all had to get out," Verniers told CNN. "There was a lot of smoke."
The Belgian crisis center tweeted that all public transportation in the city has been closed.
"Stay where you are," it said.
Kristalina Georgieva, the vice president of the European Commission, said that all the organization's institutions are at "alert level orange" and that all meetings on its premises and outside have been canceled. She advised people to stay at home or indoors.
Abdeslam, who authorities say was involved in the Paris terror attacks last year, was arrested in the Brussels suburb of Molenbeek on Friday. Belgium's Prime Minister deflected a question about whether there's any link between Tuesday's bloodshed and Abdeslam's capture, saying it is too early to tell.
He said Tuesday that he had "no information" about who was responsible for the attack, adding that authorities will find that out, but right now their focus is on caring for the victims.
Belgian national soccer team captain Vincent Kompany tweeted that he was "horrified and revolted (that) innocent people (are) paying the price again," but he urged people not to encourage those wishing to lash out.
"We must reject hate and its preachers," Kompany said. "... I wish for Brussels to act with dignity."