ISIS claimed responsibility for coordinated attacks that killed at least 31 people and injured at least 230 more in Belgium on March 22.
The attacks included suicide bombers who set off their payloads at the Brussels airport and a bomb that ripped through the Maelbeek metro station, a subway stop not far from the city's U.S. Embassy and European Union office building.
"The Metro was leaving Maelbeek station for Schuman when there was a really loud explosion," witness Alexandre Brans, 32, told The Associated Press as he wiped blood off his face. "It was panic everywhere. There were a lot of people in the Metro."
Street-level video showed plumes of smoke rising from the subway entrance as confused bystanders looked on, while video from within the subway showed authorities helping people off a train through a haze of smoke and dust.
The bombings followed the high-profile arrest of Salah Abdeslam, the Belgian-born French national who was Europe's most wanted man and an alleged planner of the November 2015 terrorist attacks in Paris, CNN reported. That attack claimed 130 lives and left more than 360 people injured or maimed.
Like the Paris strikes, ISIS leaders claimed responsibility for the airport and subway bombings in Brussels, renewing fears that the group will continue to target major urban centers in Europe. Belgium had already been on high alert, with its government warning citizens that the country was a target.
"What we feared has happened," Belgian Prime Minister Charles Michel said, per CNN. Michel urged Belgian citizens to "be calm and show solidarity."
Within hours, authorities were already hunting down suspects they believe are responsible for planning the bombings. In the northeast Brussels neighborhood of Schaerbeek, police closed down a train station and executed raids in nearby buildings. One raid turned up a nail bomb, chemicals and an ISIS flag, CNN reported.
While authorities haven't indicated whether any of the subway bombers survived, they released still images from security cameras at Brussels airport, showing three men pushing luggage carts side by side. Two of the pictured men died when they set off their suicide bombs, police said, but they believed the third man had survived and was still at large. As of late afternoon, they were asking for the public's help to identify the suspect.
Airport passenger Jerome Delanois told The New York Times he was in an Internet cafe inside the airport, near the Delta Airlines counter, when the bombs detonated.
“There were two explosions -- one big one and one little one,” Delanois said. “The first one blew all the walls and everything. There were burning flames. The first one was bigger. It blew out all the windows.”
Photographs from the scene showed shocked and injured travelers covered with blood, some of them with clothes torn or burned off, with shattered glass, rubble and pieces of the terminal's walls scattered around them.
In claiming responsibility, ISIS leaders blamed Belgium for participating in U.S.-led coalition airstrikes against ISIS targets in Iraq. Johan Verbeke, Belgium's ambassador to the U.S., said the terrorist attack would not dissuade Belgium from continuing the airstrikes.
"There is no way that intimidation will be rewarded," Verbeke said, reported CNN.
Richard Medic, a bystander who was standing outside the metro station, said he wasn't surprised by the attacks.
"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."