Belgium releases sole suspect charged over Brussels attacks

"The indications that led to the arrest of Faycal C. were not substantiated by the ongoing inquiry. As a result, the subject has been released by the examining magistrate," the federal prosecutor's office said in a statement, without giving further details.

More than 30 people were killed and 270 others injured in the attacks that hit the city's main aiport and a busy metro station. The Islamic State group claimed the attack. 

Belgian police earlier on Monday released some of the CCTV images of the bombers in a bid to identify the suspect. 

In the video, a man in a hat and white jacket is seen pushing a trolley with a large bag through the departure hall next to confirmed bombers Ibrahim El Bakraoui and Najim Laachraoui.

The third man was thought to have driven the other pair to the airport in a taxi ahead of the deadly attack.

Belgian media had initially identified the man as Faycal Cheffou, who claimed to be a freelance journalist. 

Cheffou was charged on Saturday with "taking part in a terrorist group, terrorist murder and attempted terrorist murder" before the charges were dropped on Monday.

Cheffou was known to police. According to Reuters, he served a prison sentence in 2003 when he was 18 for criminal association and complicity to murder.

He had reportedly become increasingly radicalised in recent years and had been flagged up by charities working with asylum seekers in Brussels late last year after he attempted to recruit asylum seekers from a park where they were sheltering in tents.