Three explosions on Tuesday morning killed 34 people at the airport and a busy central Brussels metro station, prompting a lockdown of the Belgian capital and heightened security across Europe.
European security officials have been bracing for a major attack for weeks, and warned that the Islamic State group was actively preparing to strike.
The arrest on Friday of a key suspect in the November attacks in Paris heightened those fears, as investigators said many more people were involved than originally thought, and that some are still on the loose.
Here is how the attacks have been linked:
November 13, 2015: A series of explosions killed at least 129 people and 350 were wounded after gunmen and suicide bombers unleashed terror at a concert hall, restaurants and the national sports stadium in Paris.
November 18: Belgian extremist Abdelhamid Abaaoud, 27, suspected of masterminding the deadly attacks in Paris, dies along with his female cousin in a police raid in the Paris suburb of Saint-Denis. A third body is later found and eight people are detained.
November 21:Brussels is placed in lockdown, remaining at maximum alert over information about an “imminent threat”, possibly a series of co-ordinated attacks at different locations.
November 22: Some 19 raids are carried out in Molenbeek, home to many of the Paris attackers, and other boroughs of Brussels, and there are three raids in Charleroi. A total of 16 people are arrested.
November 26: Belgian authorities raid three more places outside of Brussels which they say are linked to the Paris attacks, but make no arrests. The Belgian terror threat is lowered to the second-highest level in the capital Brussels, with officials calling a threat “possible and likely”.
December 3: Two more suspects are arrested. A French national, identified only as Samir Z, is detained at Brussels national airport as he bids to fly to Morocco. A second man, identified as Pierre N, is arrested during a raid only hours after the detention at the airport.
December 10: Prosecutors find Paris suspect Salah Abdeslam’s fingerprint during a search of an apartment in Schaerbeek, Brussels. They believe it served as a bomb factory for the Paris attacks. Three handmade belts which could have been intended to transport explosives, as well as bomb-making equipment, traces of TATP explosive residue and a fingerprint from Abdeslam were found there, the federal prosecutor’s office says.
December 24: Belgian authorities arrest a ninth suspect linked to the Paris attacks, a Belgian citizen born in 1985 they say had been in contact with the suspected ringleader’s cousin.
March 18, 2016: Salah Abdeslam is wounded in the leg and captured by Belgian police in a raid in the Molenbeek district of Brussels after four months on the run. Two other men are also arrested.
March 22: Just days after Abdeslam is captured, Brussels is hit by attacks on Zaventem airport and the city’s metro system, near a station close to European Union buildings.
Image: People leave the scene of explosions at Zaventem airport near Brussels, Belgium. Photograph: Francois Lenoir/Reuters