A series of explosions rocked Brussels Tuesday morning, leaving at least 30 people dead and 170 injured in the latest major terror attack to strike in the heart of Europe.

The Islamic State group claimed responsibility for the coordinated bombings, which began as two airport blasts followed by another bomb on a subway train in the middle of rush hour.

The attacks happened days after the lone surviving suspect in November's Paris attacks was captured in the city after four months on the run.

The bombings prompted an immediate security tightening around Europe and in the U.S. as well, including a stepped-up police presence at airports and on public transit. Washington's Metro system said it would increase K9 sweeps and patrols on Tuesday, but stressed that there was "no known, specific or credible threat."

Two explosions occurred just outside the security gate at Brussels' major airport. The third blast, about an hour later, struck the Maelbeek metro station near the European Union.

Officials later neutralized another bomb discovered at the airport.

Belgian authorities released an image of three possible suspects. Two men dressed in black and seen pushing carts are believed to have blown themselves up. The third, dressed in a light jacket, is thought to have escaped and is the subject of a massive manhunt, the BBC reported.

Al Jazeera English tweeted out a picture of people fleeing the airport in the midst of the terror.

The metro and tram systems were closed and the terror alert in the city was raised to its highest level.

Salah Abdeslam was arrested Friday in Brussels almost four months after a string of violence in Paris killed more than 100 people. He faced questioning over the weekend from a hospital bed in Brussels after being shot in leg during his capture.

President Obama, speaking from Cuba, pledged solidarity with Belgium and vowed to do "whatever is necessary" to bring the perpetrators to justice. French President Francois Hollande told all of Europe to prepare for a "long war" against terrorism.

Speaking after the bloodshed in his own country, Hollande declared: "Terrorism has struck Belgium but in fact it's Europe that was probably the target."