New Delhi, (PTI) In the midst of heightened Indo- Pak tensions, a Pakistan High Commission staffer was detained by police for accessing sensitive defence documents while running a spy ring for ISI, and was immediately declared persona non-grata today.

The staffer Mehmood Akhtar, who worked in the visa section of the High Commission and has diplomatic immunity, was procuring critical details including about deployment of BSF personnel along the Indo-Pak border from two other accomplices who have been arrested here, police said.

Described as the kingpin of the spy ring, 35-year-old Akhtar belongs to the Baloch regiment of Pakistani Army and was on deputation to spy agency ISI since 2013, investigators said, adding they also probing possible involvement of more people from the Pakistani mission.

Sources in Delhi Police also did not rule out possible involvement of some BSF personnel in the racket as they believe the staffer Mehmood Akhtar and his accomplices could not have got hold of deployment details unless somebody in BSF was leaking them.

Akhtar and two others -- identified as Subhash Jangir and Maulana Ramzan-- were picked up from Delhi Zoo yesterday at around 10 AM. Akhtar was released after around three hours of interrogation as he enjoys diplomatic immunity.

A fourth person Shoaib, who is a Jodhpur-based passport and visa agent, was detained by Rajasthan police this evening and was being brought to Delhi.

Shoaib was present at the meeting at the Delhi Zoo yesterday but had managed to give a slip to police.

A Delhi court sent Jangir and Ramzan to 12-day custody of the police which said their custodial interrogation was needed to unearth the larger conspiracy.

"The accused were involved in espionage activities for over a year-and-a-half. We were watching their activities for past six months. On a specific input, they were held yesterday. Akhtar is a kingpin of the spy ring," Joint Commissioner of Police (Crime Branch) Ravindra Yadav told a press conference.

Shortly after the police disclosure, Foreign Secretary S Jaishankar summoned Pakistan envoy Abdul Basit to his office and conveyed to him that Akhtar has been declared persona non-grata for espionage activities. Later, External Affairs Ministry Spokesperson Vikas Swarup said Akhtar has been given 48-hours to leave the country.

Police said that Akhtar initially showed an Aadhar card in the name of Mehboob Rajput.

"He claimed to be a resident of Chandni Chowk but after sustained interrogation, he revealed his real name Mehmood Akhtar," said Yadav.

"He is serving with Pakistan ISI and has got diplomatic immunity since he is posted in the Pakistan High Commission (PHC) of Delhi. This was verified through MEA and after confirmation and as per the due procedures, he was handed over to the PHC diplomats in presence of MEA representative," Yadav said. .