Four of six men arrested on Friday over last month's attacks in Brussels have been charged with terror offences.
The four include key suspect Mohamed Abrini, who was also wanted in connection with the attacks in Paris that killed 130 people last November.
The prosecutors could not confirm whether Abrini was the "man in the hat", the third bomber seen in a video clip in the Brussels airport attacks.
The attacks on the airport and a metro station left 32 people dead.
Officials believe those who carried out the Brussels and the Paris attacks were part of the same network backed by so-called Islamic State.
Abrini, 31, had previously not been directly linked to the Brussels bombings. His fingerprints and DNA were found in two "safe houses" in Brussels, as well as in a car used during the Paris attacks, investigators say.
Besides Abrini, those charged on Saturday were named as Osama K, Herve BN, and Bilal EM.
They are all accused of "participating in terrorist acts'' linked to the Brussels bombings. Two other people arrested on Friday have been released.
Osama K - identified in media reports as Swedish national Osama Krayem - was the man seen with the suicide bomber at Malbeek metro station just before the attack on 22 March, investigators say.
They also say that he bought bags used by the two bombers who struck at Zaventem airport on the same day.
Osama K is believed to have entered Greece from Syria with migrants last year, using a fake Syrian passport. Prosecutors believe he was driven from Germany to Belgium by Paris attacks suspect Salah Abdeslam in October.
Abrini, a Belgian national of Moroccan origin, is thought to have been filmed at a petrol station with Abdeslam two days before the attacks in Paris.
Herve BM, described as a Rwandan national, and Bilal EM are both suspected of having offered assistance to Abrini and Osama K.
Also on Saturday, heavily armed police carried out a search in the Etterbeek area of Brussels. The target was a flat which police believe may have been used as a safe house by the militants.