The operations started discreetly late on Sunday in Thane's Mumbra town and in Aurangabad, both having a dominant minority population.

While four were picked up from Mumbra, the rest were caught from Aurangabad and have been brought to Mumbai since for questioning.

Already on the ATS radar after a tip-off passed by the Centre, the sources said that the four Mumbra men were reportedly en route to Aurangabad to participate in a seminar organised by the Kerala-based Popular Front of India (PFI).

On their questioning, the ATS got details of five others based in Aurangabad, who were also picked up and detained. All of them are in the age group of 18-22.

The ATS officials claimed they have found certain objectionable material on the social media accounts of one of the detenus and now the investigators were scanning the phones, laptops, emails, social network sites and other details of all those detained.

Suspecting them for being part of sleeper cells of certain global terror groups, the ATS has also carried out raids at various premises since the past three days, but details have not been available.

The operation was the result of a high-alert in the state in preparations for the Republic Day celebrations on Saturday with multiple central and state agencies coordinating their intel inputs.