Spanish police investigating the March 2004 train bombings in Madrid arrested 13 people Friday suspected of being linked to Islamic militancy, the Interior Ministry said. A Syrian man, 39-year-old Mohamad Bassem, was detained in Madrid Friday as part of the same operation in which a dozen people had been arrested earlier in the day, an Interior Ministry source said. Four of those arrested earlier were believed to be connected to Youssef Belhadj, suspected of being a spokesman for al Qaeda who claimed responsibility for the Madrid train bombings and who was extradited to Spain from Belgium Friday, the ministry said. The other detainees were believed to be connected to Serhane ben Abdelmajid Farkhet, known as "The Tunisian," a suspected ringleader of the March 11 attacks. "The Tunisian" was among seven suspects who blew themselves up in a suburban Madrid apartment on April 3 rather than face arrest. In Friday's operation police arrested six Moroccans, four Syrians, an Egyptian, a Palestinian and an Algerian in raids which started before dawn in Madrid and its suburbs. One of the suspects is considered "The Tunisian's" personal assistant, the ministry said. The operation, part of the investigation into the attacks which killed 191 people in March last year, remains open. Friday's swoop brings to about 90 the total number of arrests since the attacks on four commuter trains. Most of them are of North African origin and 45 remain in jail or under court supervision. Belhadj appeared briefly before a Spanish judge in Madrid on Friday after being extradited and was accused of the murder of 191 people and belonging to an armed group, a court source said.