Three people were arrested by the Kolkata Police's Special Task Force (STF) on Sunday for allegedly spying for Pakistan, an officer said.
The three - Irshad Ansari, Asfaq Ansari and Mohammad Jahangir - were rounded up from the city's Ekbalpore area.
"Besides fake Indian currency notes of face value of Rs.5 lakh, several incriminating documents have been seized from them," STF's Deputy Commissioner Akhilesh Charurvedi said.
Chaturvedi said a map of the Defence PSU GRSE that builds ships for the the Indian navy was seized from one of the accused.
"The three had earlier gone to Pakistan where they were suspected to have been hired by the ISI (Pakistan's spying agency)," said the officer, adding they seemed to be Indian nationals.
The STF is also probing the three people's involvement with Mohammad Ejaz who was arrested on Friday from Uttar Pradesh for being a suspected ISI agent.
They will be presented before a court on Monday.
Earlier this month, Kolkata STF had arrested suspected ISI agents Akhtar Khan and his brother Zafar Khan from the city.