The two boarded the military compartment of the Kamrup Express wearing 'army uniform' last night, but actual army personnel inside the coach found discrepancies in their uniform, they said.
Police said they challenged the two, identified as Rashid Ahmed and Mohammand Aslam, and soon found out that they were not armymen and were carrying 16 kg brown sugar to Assam.
They were then handed over to police.
During interrogation, they revealed that they had been ULFA militants and surrendered in 2011, police said.