At least 200 people, mostly activists of the Students Islamic Movement of India, have been detained from Mumbai and various parts of Maharashtra by the Anti-Terrorism Squad for questioning in connection with Tuesday's serial bomb blasts in the city, police said on Wednesday.

In an overnight drive by city police, railway stations, lodges and hotels were searched and suspected SIMI activists were rounded up from their homes, sources said, adding that the detained people will be interrogated to collect clues regarding the blasts.

ATS chief K P Raghuvanshi told PTI that several persons have been rounded up on Wednesday night, but no one has been arrested yet. "It is a routine procedure of investigation and the detained will be interrogated in connection with the blasts," Raghuvanshi added.

Sources in office of the state Director General of Police office said similar searches were conducted at hotels and lodges and activists of the Islamic student body rounded up from various parts of Marathwada and Konkan regions, which are regarded as SIMI strongholds.

Over 200 people were killed and another 750 were injured in seven blasts that ripped off first class compartment of western railway suburban trains on Tuesday evening. Police suspect that the bombs were placed in leather bags and kept in luggage racks, and went off in a span of 20 minutes.