Belgian prosecutors have charged a man with terrorist offences, in relation to the deadly attacks in Brussels that left 31 dead.
They named him as Faycal C, who was arrested on Thursday.
Suicide bombings, claimed by so-called Islamic State (IS), killed 11 people at Zaventem airport on 22 March, while 20 people died in an attack on the metro.
Zaventem – Brussels international airport – will not reopen before Tuesday, authorities have announced.
Separately, the authorities have appealed for a “march against fear” planned for Sunday to be postponed, citing concerns that it could divert police resources away from the investigation.
Belgian prosecutors said that Faycal C had been detained outside the prosecutor’s office in Brussels on Thursday. A search of his home had found no weapons, a statement said.
It said Faycal C was charged with “participation in the activities of a terrorist group, terrorist murders and attempted terrorist murders”.
It gave no further details and made no comment on Belgian media reports that he was the third man in an airport CCTV image along with two suicide bombers, Najim Laachraoui and Brahim el-Bakraoui.
Brahim’s brother, Khalid el-Bakraoui, carried out the Maelbeek metro attack.
Faycal C was among 12 people arrested on Thursday and Friday in police raids in Belgium, France and Germany.
Four days before the Brussels attacks, the key suspect in the 13 November Paris attacks which killed 130 people, Salah Abdeslam, was detained in a raid in Brussels. Police said he was initially co-operative.
But Belgian Justice Minister Koen Geens later confirmed in parliament that Abdeslam “no longer wants to talk since [Tuesday’s] attacks” in Brussels.