Bilateral relations between South Asian neighbors India and Pakistan remain tense with a Pakistan high commission staffer being detained by the Delhi Police for espionage after Indian authorities discovered border area maps and documents on defense deployment.

According to local media reports, 35-year-old Mehmood Akhtar was held for spying after he was found with highly classified army-related documents. Akhtar worked as a part of Pakistan envoy  Abdul Basit's staff  and was reportedly being tailed by India’s Intelligence Bureau for a week.

While the staffer — who had been working with the high commission for three years — has been released due to diplomatic immunity, he has been “declared persona non grata for espionage activities.” Basit has been summoned by India’s  external affairs ministry but reports suggest that he has denied any such allegations.

“The Pakistan high commission official was the kingpin. He used to recruit Indians for spying and send information to Pakistan… The (spying) module was active for one-and-a-half years. We were working (to bust) it for the past six months,” Delhi police joint commissioner Ravindra Yadav said, according to local newspaper Hindustan Times. “We recovered documents on defense deployment and border area maps. They had lists of BSF men who were deployed, transferred or retired.”

Two Indian citizens — identified as Maulana Ramzan and Subhash Jangir — from the border state of Rajasthan were also apprehended by the authorities and have been booked under the Official Secrets Act.

The relations between the neighboring countries have been strained following an attack on an Indian army base in Uri, Kashmir, which resulted in the killing of 19 soldiers. India has accused Pakistan-based militants of carrying out the attacks, and reportedly retaliated with “surgical strikes” across the line of control. Pakistan has denied that any such raids were carried out, asking India to produce credible evidence to back its claim.

India has repeatedly accused Pakistan of funding infiltration attempts into the country, while Islamabad has sharply criticized India’s repeated human rights violations in the border state of Kashmir.