The two Chinese nationals arrested earlier this week from the Bagdogra airport in West Bengal appear to be "tough spies on a specific mission", Indian intelligence officials said.

Until late Friday, the two have not broken up and coughed out anything despite persistent questioning, the officials said.

"Both pretend not to understand our questions. We are under orders not to use third degree, so they are getting away, but we have to find a way to break them," one intelligence official said.

What worries Indian intelligence is the recovery of two forged Aadhaar cards with Uttar Pradesh addresses.

"The Aadhar card seems to be turning into a joke. Looks like anybody can procure it," the official said, adding: " There must be a support network in India to back up these Chinese agents with documentation, ticketing and much else."

Police in Bagdogra near Siliguri had earlier said that the two Chinese were arrested on Tuesday for travelling without any documents and booked for illegal trespass.

(IANS)