The Belgian authorities were warned one of the Brussels killers was a terrorist - but he was allowed to walk free, Turkish officials have said.
Ibrahim El Bakraoui, one of the suicide bombers who killed 14 people at the airport, was caught in June at the Turkish-Syrian border and deported to the Netherlands, Turkey said.
The Turkish authorities said they warned Belgium and the Netherlands he was a "foreign terrorist fighter", but the Dutch authorities let him free because the Belgian authorities could not link him to terrorism.
Turkish president Recep Tayyip Erdogan said that "despite our warnings that this person was a foreign terrorist fighter, Belgium could not establish any links with terrorism".
The revelation comes as new reports say Najim Laachraoui, who was believed to be the "man in white" and on the run, was in fact the second suicide bomber at the Brussels airport.
News agency AFP and the Washington Post reported that they had been told by sources that Laachraoui, 24, blew himself up at the airport.
The reports have not been confirmed by the Belgian authorities, but if true it means the identity of the "man in white" who is believed to have fled after dumping a bag of explosives, remains a mystery.