REUTERS - Police have arrested a man who was seen on security footage next to Khalid El Bakraoui, the suicide attacker who detonated a bomb in the Brussels metro, De Standaard newspaper reported on Friday.
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The federal prosecutor's office did not confirm the arrest.
De Standaard newspaper said the man, whom it did not name, was arrested after a policeman recognized him from the security footage.
Khalid El Bakraoui, 27, who blew himself up on a crowded rush hour train, is the brother of Brahim El Bakraoui, who detonated a bomb at Brussels Airport an hour earlier.
The joint attacks killed at least 31 people and wounded 316.
Public broadcaster RTBF meanwhile reported police detained a seventh person in the district of Forest following six arrests late on Thursday, while authorities in France said they thwarted a militant plot there "that was at an advanced stage."
The federal prosecutor's office in Belgium said that the arrests came during police searches in the Brussels neighborhoods of Schaerbeek in the north and Jette in the west, as well as in the center of the Belgian capital.
The attack in Brussels, which is home to the European Union and NATO, has heightened security concerns around the world and raised questions about European countries' response to the threat from Islamist extremists.
The Islamic State militant group, which claimed responsibility for the Brussels bombings, also took credit for coordinated attacks in Paris in November that killed 130 people at cafes, a sports stadium and concert hall.
In Paris on Thursday, authorities arrested a French national suspected of belonging to a militant network planning an attack in France.
French Interior Minister Bernard Cazeneuve said in a televised address that the arrest helped "foil a plot in France that was at an advanced stage."
Cazeneuve added that the man arrested "is suspected of high-level involvement in this plan. He was part of a terrorist network that planned to strike France."
After the arrest by the French counterterrorism service, DGSI, the agency raided an apartment building on Thursday night in the northern Paris suburb of Argenteuil. French TV station ITele reported that explosives had been found in the man's house.
"At this stage, there is no tangible evidence that links this plot to the attacks in Paris and Brussels," added Cazeneuve, who was in the Belgian capital earlier on Thursday.
Earlier on Thursday, Belgium's interior and justice ministers offered to resign over a failure to track an Islamic State militant expelled by Turkey as a suspected fighter and who blew himself up at Brussels Airport.
Brahim El Bakraoui was one of three identified suspected suicide bombers who hit the airport and metro train. At least one other man seen with them on airport security cameras is on the run and a fifth suspected bomber filmed in the metro attack may be dead or alive.
Bakraoui's brother Khalid, 26, killed about 20 people at Maelbeek metro station in the city center. De Morgen newspaper said he had violated the terms of his parole in May by maintaining contacts with past criminal associates, but a Belgian magistrate had released him.