A special NIA court on Thursday remanded peasant leader Akhil Gogoi, who had been arrested by the agency, to judicial custody for 14 days.
The special court also turned down NIA's plea to extend his custody for 10 days.
He was arrested by the National Investigation Agency (NIA) from Jorhat on December 12 when large scale protests against the Citizenship Amendment Act was rocking Assam under the stringent Unlawful Activities (Prevention) Act.
Earlier in the day the NIA searched the residence of Gogoi, who is also an RTI activist, at Nizarapara area and seized several documents and a laptop computer, officials said.
The Krishak Mukti Sangram Samiti (KMSS) leader, whose NIA custody was to end on Friday, was brought from New Delhi and produced before the court. Gogoi was instrumental in mobilising protests across several districts in upper Assam against the contentious Citizenship (Amendment) Act.