"The madness of men is what it is but peace must win over."
The statement from prosecutors said the investigation "is continuing actively day and night.''
Perpetrators were "surprised by the speed of the progress in the ongoing investigation'' and decided to rush an attack on Brussels instead.
Airport officials suggested the first flight out was a symbolic victory over those who sowed death and hate.
The report said two of the men were known to police.
For the first time in its history, Belgium has raised its terror threat to its highest level.
Belgian officials said the casualty toll from three explosions in the capital was 26 dead and at least 136 injured.
The Paris airport authority said security was tightened at all Paris airports soon after the Brussels explosions on Tuesday
Twenty-three students from Sir Charles Tupper Secondary and their chaperones were in Ghent, about 35 kilometres outside Brussels.