
Photo from DR
News outlets, quoting judicial sources, had named him as Najim Laachraoui, possibly seen in a CCTV image before the Zaventem airport blasts. But media later said that a man detained in the district of Anderlecht was not Laachraoui, the BBC said.
Twin explosions at the airport and another at a metro station on Tuesday left about 34 dead and 250 wounded.
Two of the other attackers have been named in Belgian media as the brothers Khalid and Brahim el-Bakraoui.
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Belgium is observing three days of national mourning and held a minute's silence for the victims at midday (11:00 GMT).
So-called Islamic State (IS) has said it was behind the attacks and warned that more would follow.