Amid growing strain in relations, India and Pakistan today declared a staffer each at their High Commissions in New Delhi and Islamabad persona non-grata and sought their recall in tit-for-tat action after Indian police busted an ISI-run spy ring involving an employee of the Pakistani mission.

Mehmood Akhtar, who worked in the visa section of the High Commission and had diplomatic immunity, was procuring critical details including those about deployment of BSF personnel along the Indo-Pak border from two other accomplices who were arrested in Delhi, 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.

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.

India asked Akhtar to leave the country within 48 hours.

“Today morning Foreign Secretary S Jaishankar summoned the Pakistan High Commissioner Abdul Basit and informed him that India had intercepted an official of the Pakistan High Commission in the pursuit of espionage and that he was being declared persona non-grata,” Ministry of External Affairs Spokesperson Vikas Swarup said.

“The Pakistan High Commission has been informed that Mehmood Akhtar and his family must return to Pakistan by October 29. The Foreign Secretary also strongly conveyed to the Pak High Commissioner that the Pak High Commission must ensure that none of its members indulge in activities inimical to India, or behave in a manner that is incompatible with their diplomatic status,” Swarup said.

In swift tit-for-tat action, Pakistan also declared an Indian High Commission official as persona non-grata and asked him to leave the country within 48 hours.

A Pakistan Foreign Office statement said the decision was conveyed to Indian High Commissioner Gautam Bambawale who was summoned to Foreign Ministry in Islamabad.

“The Foreign Secretary (Aizaz Chaudhry) summoned the Indian High Commissioner today and conveyed the decision of the Government of Pakistan to declare Surjeet Singh, an official of the Indian High Commission, as persona non-grata,” the statement said.

The Foreign Secretary expressed deep concern over the activities of the Indian official that were in violation of the Vienna Convention and the established diplomatic norms, it said.

The Indian High Commission has been asked to make urgent necessary arrangements for Singh and his family to leave Pakistan by October 29.