Three explosions at two main transit hubs in the Belgian capital of Brussels early Tuesday left at least 31 dead and scores injured.

The Islamic State claimed responsibility for the attacks, attributing it to a "security group from the soldiers of the caliphate," reports the Los Angeles Times.

The group chose their sites "carefully" and were "wrapped in explosive belts and carrying explosive canisters and machine guns," it said in a statement.

"What is coming is worse and more bitter Allah permitting," it warned. "Thanks be to Allah for his accuracy and success, and we ask Allah to accept our brothers among the martyrs."

The first attack came at roughly 8 a.m., when two explosions hit Brussels Airport, sending terrified passengers fleeing during one of the busiest times of the day. Around an hour later, an explosion struck the Maelbeek metro station, located near the political hub of the city and close to European Union institutions. A suicide bomber was responsible for at least one of the explosions, the Brussels public prosecutor said, according to Belgian radio.

Officials reported that 14 were killed and 81 were injured at the airport. Twenty others were killed at Maelbeek station, Brussels Mayor Yvan Mayeur told Belgian media. The country declared three days of national mourning.

The incidents come four days after one of the suspects in November's fatal Paris terrorist attacks, Salah Abdeslam, was apprehended in Brussels after four months on the run.

Authorities said Abdeslam had helped create a jihadist network centered in the city and had been planning a fresh attack. A large cache of weapons had been discovered when he was captured, officials said. They also had warned of possible retaliatory attacks and said other terrorists were on the loose.