Media reports say two of the suicide bombers who carried out attacks in Brussels on Tuesday have been named as brothers Khalid and Brahim el-Bakraoui, Belgian nationals.
The federal prosecutor said Brahim was part of the attack at Zaventem airport that killed 11 people. Khalid struck at Maelbeek metro, where 20 people died.
Two other attackers at the airport have not yet been identified. One of them died, another is on the run.
Belgium is observing three days of national mourning.
So-called Islamic State (IS) has said it was behind the attacks.