This is a special CNN Breaking Newsletter.
Three explosions that ripped through the Belgian capital of Brussels on Tuesday 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.
President Obama condemned the attacks during a speech in Havana, Cuba, saying that the United States stands in solidarity with Belgium.
"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.
Here’s what we know at this hour:
THE ATTACKS
Airport: At around 8am local time, two explosions ripped through the departure lounge of Zaventem airport. At least one of those explosions was a suicide bombing, according to a Belgian prosecutor.
At least one of the blasts took place outside the security checkpoints for ticketed passengers and near the airline check-in counters, according to an airline official.
Metro Station: About an hour after the airport explosions, there was an explosion at the Maalbeek metro station in the heart of Brussels, where European Union institutions are based.
THE INVESTIGATION
Evacuation: A nuclear power plant in eastern Belgium has been evacuated, aside from essential staff, under an order from Belgian authorities, a representative of the company that operates the plant said.
Details about why the order was given weren't immediately available.
Raids: Police raids are happening in the Brussels region, with authorities looking for people suspected of being linked to Tuesday's deadly explosions, Belgian broadcaster RTBF reported.
Airport discovery: Belgian media report a Kalashnikov assault rifle was found in the departure hall of the Zaventem airport in Brussels.
Suitcase bomb?: Investigators are looking at the possibility that one of the Brussels airport explosions may have been caused by a bomb inside a suitcase.
Working theory: Investigators suspect the attack was one of opportunity, targeting a large group of people in an area near airline ticket counters, two officials say. There's no indication so far that the attacker tried to go past the security screening checkpoint, but authorities are continuing their investigation, including reviewing surveillance footage to be sure, the officials say.
GLOBAL RESPONSE:
U.S. security: Authorities in Washington, New York, Chicago and other cities are taking special precautions, such as increased K-9 sweeps of subways and additional police patrols. The FBI is also boosting checks on the whereabouts of suspected extremists who are already being monitored and checking for any intelligence indicating possible threats in the United States, officials say.
Additionally, U.S. national security officials are on guard for possible copy-cat attacks, though there is no specific indication of any plots in the United States tied to the Brussels attacks, officials said.
U.K. security: British police have increased their presence at certain locations, including transport hubs like London's Heathrow and Gatwick airports, according to Scotland Yard.
NATO security: The alliance, which is headquartered in Brussels, is increasing its level of alert in the wake of the bombings in the city, it said in a statement.
THE BACKDROP:
U.S. intelligence officials say they weren't surprised about an attack in Brussels because there have been general concerns about terror threats there, particularly in the wake of recent raids and the arrest of key Paris attacks suspect Salah Abdeslam last week.
Belgium has been a top concern for counterterrorism officials for years because of the large number of Belgian foreign fighters who traveled to join ISIS and other terror groups in Syria and Iraq and then returned to Europe.
Get complete coverage of Belgium terror attacks and other breaking news on CNN TV,
CNN.com and CNN Mobile.
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