Officials in Belgium say 15 suspected Islamic militants have been arrested as part of a Europe-wide investigation. All 15 are foreigners.
There has been no confirmation from Belgium that the arrests are in connection with the Madrid train bombings, in which almost 200 people died last March.
Earlier, authorities in Spain and Italy said a man arrested in Milan last night was one of the masterminds of the bombings.
The man was named as Rabei Osman Sayed Ahmed and was known to police as 'Mohamed the Egyptian'. A number of others were also arrested.
It is believed Ahmed was the head of a group of Moroccan militants but may himself be Egyptian.
The Italian Interior Minister, Giuseppe Pisanu, said the militants were planning more attacks when the police moved in.
20 people have been accused of involvement in the Madrid bombings. 14 of them are under arrest, while at least 20 others have been arrested and cleared.
