A series of deadly explosions rocked Brussels on Tuesday, targeting the Belgian capital's main airport and metro system.

Belgian officials said the airport and subway bombings killed at least 31 people and injured nearly 200, according to reports. They raised the terror threat level and shut down public transit.

Belgian Prime Minister Charles Michel called Tuesday a dark moment for the country.

"What we feared has come to pass. Our country has been struck by attacks which are blind, violent and cowardly," Michel told a news conference.

Two explosions, one of which was likely a suicide attack, hit Zaventem airport's main departure hall, NBC News reported. Photos from the scene showed injured victims and debris. Trains to the airport were suspended, VRT said, and the airport was evacuated and all flights suspended.

Following a blast at the metro station of Maelbeek, close to the European Union institutions in central Brussels, the city's public transport authority said all metro stations were closed. The crisis center tweeted: "Stay where you are."

The Belgian ministry of health said the airport bombing killed at least 11 people and left 81 injured. Yvan Mayeur, the mayor of Brussels, said 20 people were believed dead and 106 injured in the metro bombing.

Deputy Prime Minister Didier Reynders said no information suggested the attack was linked to the arrest of Salah Abdeslam, a suspect in last year's Paris attacks, in Brussels. The so-called Islamic State claimed responsibility for the attack, according to reports, citing a news agency affiliated with the terrorist group.

Belgian police are searching a residence that may have served as a staging ground for the attack, a senior US intelligence official told NBC News. Officials are still trying to determine whether another attack is imminent.

Speaking in Cuba on Tuesday morning, U.S. President Barack Obama pledged to support Belgium in bringing the attackers to justice.

"We stand in solidarity with them, condemning these outrageous attacks against innocent people," he said.

Obama spoke with Michel on Tuesday, offering assistance in investigating the attacks, the White House said.

Eye witness Charlotte Van Driessche, who was on the metro behind the one under attack, told public broadcaster VRT: "We heard a loud bang … there was chaos immediately as everyone suspected the attack was linked to the blast in Zaventem …There was a huge amount of panic ... There was a terrible smell, a real smell of burning."

Photos posted on Twitter show significant damage to the airport. VRT said at least one of the explosions happened near the check-in desks for American Airlines. American Airlines told CNBC in an e-mailed statement it had accounted for all of its employees and contractors with no reported injuries.

Belgian news agency Belga said shots were fired and Arabic was shouted before the two explosions, Reuters reported.

tarbucks said initial indications showed a blast went off near one of its stores in the airport. The company said one employee was injured and it has accounted for all other workers.

The Mormon church also said three missionaries were injured in the airport blast. They were listed in critical condition.

Belgium has been on high terror alert since the Paris attacks on Nov. 13. The blasts come four days after the capture of Abdeslam.

Former French Prime Minister Dominique de Villepin told CNBC that the attacks were "tragic events" but added that Europe could only "reduce" the threat of terrorism.

"I do believe that our strategy should be very different than the one it is. Much less military approach than a political approach, trying to find solutions in the Middle East and we are far from doing that," he said.

European stocks traded lower following the bombings and gold rallied. U.S. stocks also opened lower.

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First Published:Mar 22, 2016 9:23 PM IST