A Brussels-based terror cell had planned to launch fresh attacks in France, but attacked the Belgian capital instead, after being "surprised" by the quick investigation in France, Belgian prosecutors said.
"Surprised by the speed of the progress in the ongoing investigation, they urgently took the decision to strike in Brussels," Belgium's Federal Prosecution Office said on April 10.
Investigators have found links between the cell behind the Brussels attacks and the group that organized the November attacks in Paris.
On April 9, Belgian authorities charged four men with participating in "terrorist murders" and the "activities of a terrorist group" over the Brussels attacks.
One of these men is Paris attacks suspect Mohamed Abrini, who became known as the "man in the hat," based on video surveillance images from the Brussels airport shortly before last month’s’ attack.
Abrini is the last known fugitive of the Paris attacks, which killed 130 people on November 13.