The prosecutors said they were also looking into whether Abrini is the so-called “man in the hat”, the surviving third suspect seen on CCTV images next to the two suicide bombers who blew themselves up at the Brussels airport on March 22.
“We are investigating if Abrini can be identified as the third person at the Brussels national airport, the so-called man with the hat,” said prosecutor Eric Van der Sypt.
Abrini, a 31-year-old Belgian, has been on Europe’s most wanted list since the November 13 Paris attacks, in which 130 people were killed.
He was last seen two days before the attacks in a motorway service station CCTV video driving with another Paris attacks suspect – Salah Abdeslam, who was arrested last month – towards the French capital from Belgium.
The car they drove was used in the attacks, in which Abdeslam’s elder brother was a suicide bomber.
Second metro bomber?
Another man arrested on Friday, identified as Osama K, may have been present at the suicide bomb attack in the Brussels underground station of Maelbeek, prosecutors said.
The man was seen in the company of Khalid el-Bakraoui before he blew himself up in the metro, and was also filmed buying the bags used in deadly attacks that same day on the Brussels airport.
“The investigators are now verifying whether Osama K can be positively identified as being the second person present at the time of the attack in the Maelbeek subway station,” Van Der Sypt said.
Al Jazeera’s Natacha Butler, reporting from Paris, said if the metro link is confirmed, that would signal a “big scoop” for authorities.
“We know that this man was seen by the bags that the Belgian airport bombers used in their attack – they hid their explosives in luggage – so this is someone that they’ve also been looking for extremely intensively over the last few weeks,” Butler said.
Media had previously reported about a second underground attacker, but officials had not confirmed that.
The attacks on Brussels airport and a metro train last month killed 32 people and wounded hundreds in the worst such incident in Belgian history.
Islamic State of Iraq and the Levant (ISIL, also known as ISIS), which claimed responsibility for the Brussels bombings, also took credit for coordinated attacks in Paris in November .
Friday’s arrest of five suspects came a day after Belgian authorities released photos and video of the “man in the hat” airport suspect.
Five hours after the initial detentions, authorities were still carrying out a raid in the same Anderlecht area of Brussels.
The government and top security officials gathered in a national security council meeting in the wake of Friday’s detention to assess the consequences of the operation.