According to police, the mobile phone sets siezed from them had pictures of key ULFA leaders and visuals of parades conducted by the ultra outfit in parts of Assam.
The arrested were identified as Hemanth Gogoi (22), Dhaniyam Gogoi (53) and Bidyut Chedia (18), all hailing from Assam, police sources said.
They were taken into custody yesterday and their arrest recorded late in the evening.
They would be produced before the first class judicial magistrate today, sources said.
Based on interrogation, police was on the look out for a person who was believed to have given them the memory card containing ULFA visuals and group song, as part of propagation of ULFA ideology among migrant labourers.
Police also searched the worksite at Kanhirapally in the district where the arrested had been working for the last several months.
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The arrested have been charged under Section 41-A of the CrPC (reasonable suspicion of committing offence), sources said.
Construction sector in Kerala has thousands of migrant labourers from north east, mostly from Assam, Orissa and West Bengal.