Pakistan's foreign secretary summoned the Indian High Commissioner on Thursday to say the government would be expelling a diplomat.
The apparent tit-for-tat move followed New Delhi's announcement earlier in the day that it would be sending back a Pakistani diplomat it accused of spying.
"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," a statement said, naming the official as Surjeet Singh.
India earlier said it would expel a Pakistan High Commission official for "espionage activities", the foreign ministry said, with tensions between the nuclear-armed neighbours already running high.
India's foreign secretary, Subrahmanyam Jaishankar, summoned Pakistan's High Commissioner Abdul Basit to inform him of the decision to expel Mehmood Akhtar, who was briefly held in New Delhi on Wednesday.
Delhi police crime commissioner, Ravindra Yadav, said the official had been detained after defence and other documents were found in his possession.
The documents included information on the deployment of India's border security forces, Yadav told a press conference.
Two men from Rajasthan were arrested for allegedly leaking sensitive documents to Akhtar, who was let off because of diplomatic immunity.
"The Pakistan High Commission official was the kingpin," said Yadav.
"He used to recruit Indians for spying and send information to Pakistan. The [spying] module was active for a year and a half. We were working [on] it for the past six months. We recovered documents on defence deployment and border area maps. They had lists of BSF men who were deployed, transferred or retired."
A Pakistan High Commission official in New Delhi confirmed to Al Jazeera that Akhtar has been given 48 hours to leave the country.
READ MORE: India claims striking suspected rebels in Pakistan
"The High Commissioner was summoned and informed about India's decision," the official told Al Jazeera.
"Pakistan High Commission strongly denies and rejects the accusations levelled against the staff member by the India government. We strongly protested the decision as well as the detention and manhandling of our staff member.
"We also urge the government of India to ensure such harasment does not happen in the future."
