The searches in the city of Coimbatore, Tamil Nadu, came after the arrest in April of an Indian national who allegedly followed Zahran Hashim, the mastermind of April 21 bombings in Sri Lanka that killed 253 people.
India's National Investigation Agency (NIA) said in a statement that the "prime accused" in the Coimbatore case, Mohammed Azarudeen, 32, "has been a Facebook friend" of Hashim.
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It named five others aside from Coimbatore who, it alleged, were also "propagating the ideology of proscribed terrorist organisation ISIS/Daesh on social media with the intention of recruiting vulnerable youth... for carrying out terrorist attacks in South India especially in Kerala and Tamil Nadu."
ISIS and Daesh are other acronyms for the IS militants, who have carried out bombings, shootings and other atrocities around the world.
India has been concerned about militant extremists on its soil for some time and the Sri Lanka bombings left authorities alarmed that the Hindu-majority country might be at risk of an attack by militants.
Hashim was a Sri Lankan Muslim preacher who led the coordinated Easter Sunday suicide attacks on churches and hotels in Sri Lanka - one of the world's deadliest terrorist incidents.
Sri Lankan authorities blamed a local militant group, the National Thowheeth Jama'ath (NTJ), but IS claimed responsibility.
The NIA said Azarudeen maintained a Facebook page through which he propagated IS ideology, while other members of his group "have also been sharing radical contents attributed to Hashim."
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One of them has "been a close associate" of Riyas A, alias Riyas Aboobacker, 29, the alleged Hashim follower arrested by the NIA in April.
According to the NIA, Aboobacker admitted he wanted to carry out an attack in Kerala.
Officers seized mobile phones, SIM cards, computer materials and documents during the Coimbatore raids, NIA said.
The accused were being questioned in connection with that material, but in its announcement the NIA did not state any specific charges against them.
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