The attackers who struck Brussels last month had initially planned to launch a second attack on France, Belgium's Federal Prosecution Office has said.
But the group was "surprised by the speed of the progress in the ongoing investigation" and decided to rush an attack on the Belgian capital instead, the office said in a statement on Sunday.
Two suicide bombers killed 16 people at Brussels Airport on March 22. A subsequent explosion at the city's Maelbeek subway station killed another 16 people the same morning.
Investigators found links between the cell behind the Brussels attacks and the group that killed 130 people in Paris on November 13.
Sunday's statement confirmed what many had suspected: the series of raids and arrests in the week leading up to the Brussels attacks - including the capture of key Paris attacks fugitive Salah Abdeslam - pushed the killers to action.
On Saturday, Belgian authorities charged four men with participating in "terrorist murders" and the "activities of a terrorist group" in relation to the Brussels attacks.
In pictures: Brussels attacks
One of them, Mohamed Abrini, has also been charged in relation to the Paris attacks, prosecutors said.
Abrini has been identified as the so-called "man in the hat" spotted alongside the two suicide bombers who blew themselves up at Brussels Airport.
Surveillance footage has also placed him in the convoy with the attackers who headed to Paris before the November 13 attacks.
Abrini was a childhood friend of Brussels brothers Salah and Brahim Abdeslam, both suspects in the Paris attacks, and he had ties to Abdelhamid Abbaoud, the Paris attackers' ringleader who died in a French police raid shortly afterwards.
Brahim Abdeslam blew himself up in the Paris bombings while Salah Abdeslam was arrested in Brussels on March 18 - four days before the attacks there - after a four-month manhunt.
Abrini's fingerprints and DNA were not only in a Renault Clio used in the Paris attacks but also in an apartment in the Schaerbeek neighborhood of Brussels that was used by the airport bombers.
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Abrini was also believed to have travelled to Syria, where his younger brother died in 2014 as a member of the Islamic State of Iraq and the Levant's (ISIL) Francophone brigade.
The other suspects charged on Saturday were identified as Osama Krayem, Herve BM, and Bilal EM.
Krayem is known to have left the Swedish city of Malmo to fight in Syria.
Despite the arrests and charges, Brussels remains under the second-highest terror alert, meaning an attack is still considered likely.