Brussels Airport
Brussels Airport Reuters

Two brothers who carried out suicide bombings in Brussels this week were known to American government agencies before the attacks, two sources familiar with the matter told Reuters on Thursday.

The sources said that Khalid El Bakraoui and Brahim El Bakraoui were both on United States government counter-terrorism watch lists before the attacks.

Belgian prosecutors have identified Brahim El Bakraoui as one of two suicide bombers who attacked Brussels' Zaventem Airport, and they say Khalid El Bakraoui was the man who carried out a suicide bombing at Brussels' Maelbeek Metro station, near European Union headquarters.

Earlier on Thursday it was reported that the El Bakraoui brothers may have planned to bomb a Belgian nuclear plant and cause a nuclear explosion.

The Belgian newspaper La Derniere Heure revealed that the two had filmed the chief of the Belgian nuclear program with cameras hidden in bushes outside of his house in Flanders. The nuclear chief had been tracked and followed by the terrorists for a long time.

Police back in December seized the footage during a raid shortly after the Islamic State (ISIS) Paris attacks in which 130 people were murdered. The ten hours or so of video was found in the apartment of Mohammed Bakkali, another suspect in the same ISIS terror cell.

Reports have indicated that Belgium received advanced warnings of the terrorist attacks but did not act on those warnings.

Channel 2 News reported on Wednesday that Israel had provided Belgium with concrete information on security breaches at the Zaventem Airport, where the first of two attacks on the Belgian capital took place, and claimed that "there are serious security deficiencies at the airport in Brussels".

Also on Wednesday, Turkish President Recep Tayyip Erdogan said his country had warned Belgium about Brahim El Bakraoui, but Belgium failed to act on the warnings.