"The two terrorist suspects have left the Saint-Pierre hospital," Yvan Mayeur wrote on Twitter, without saying where they were taken.
Both are likely to be questioned before a hearing on their extradition to France in connection with the November attacks on Paris which left 130 people dead.
Key suspect of Paris attacks caught
Abdeslam, 26, and four other suspects were arrested on Friday in the gritty Brussels neighbourhood of Molenbeek.
During the raid, he was lightly wounded in the leg, prosecutors said.
French President Francois Hollande, in Brussels for an EU summit, hailed the arrests saying Paris would request Abdeslam's extradition from Belgium "as rapidly as possible".
Also arrested was a man known by the fake name Amine Choukri, who in addition used a false Syrian name Monir Ahmed Alaaj.
Three members of a family which sheltered Abdeslam in Molenbeek, where he lived and ran a bar with his brother Brahim, were also detained.
'You saved my life': Paris attack survivors seek solace with Bataclan security man
Brahim Abdeslam blew himself up during the Paris attacks and was buried discreetly on Thursday in a Brussels cemetery.
The arrests leave only one known suspect still on the run, Mohamed Abrini, who was filmed with Abdeslam two days before the attacks at a petrol station on a motorway close to Paris.
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