According to police, the mobile phone sets detained from them had pictures of key ULFA leaders and visuals of parades performed by the ultra group in parts of Assam.
The arrested were recognized as Hemanth Gogoi (22), Dhaniyam Gogoi (53) and Bidyut Chedia (18), all summon from Assam, police sources said.
On Wednesday, they were taken into custody and their arrest recorded late in the evening. They would be created before the first class judicial magistrate on Thursday, sources said.
Police also looked for the worksite at Kanhirapally in the district where the arrested had been working for the last some months.