The fractious relationship between the neighbours has worsened since New Delhi expelled two Pakistan embassy officials over spying claims in late May.

After that, New Delhi accused Islamabad of torturing two Indian diplomats arrested following an alleged hit-and-run in the Pakistani capital.

The men returned to India on Monday, where they "provided graphic details of the barbaric treatment that they experienced", the foreign ministry claimed.

"The behaviour of Pakistan and its officials is not in conformity with the Vienna Convention and bilateral agreements on the treatment of diplomatic and consular officials," the ministry said in a statement.

"Therefore, the government of India has taken the decision to reduce the staff strength in the Pakistan High Commission in New Delhi by 50 percent."

The ministry said it would also "reciprocally reduce its own presence in Islamabad to the same proportion".

Pakistan's foreign ministry said it "completely dismisses" allegations its staff in New Delhi had violated any diplomatic conventions.

"Pakistan also rejects the insinuations of intimidation of Indian High Commission officials in Islamabad," a Pakistan ministry statement read.

"The Indian government's smear campaign against Pakistan cannot obfuscate the illegal activities in which the Indian High Commission officials were found involved in," the statement added -- an apparent reference to a June 16 traffic incident in Islamabad that two Indian officials allegedly fled.

The Pakistan statement said it was Islamabad -- and not New Delhi -- that had ordered the reciprocal 50 percent reduction to the Indian diplomatic presence in the Pakistan capital.

Both countries said the staffing cuts must be made within seven days.

The Pakistan high commission in New Delhi was allowed up to have up to 106 personnel, but in recent months Islamabad reduced staff levels to about 80, diplomatic sources told AFP.

Tensions were already high after India in August scrapped Muslim-majority region Kashmir's semi-autonomous status and imposed a major security clampdown.

Kashmir was split between India and Pakistan in 1947 when they gained independence from Britain, but is claimed by both.

Indian government forces have also been conducting numerous counter-insurgency operations in Kashmir since a nationwide virus lockdown was imposed in late March, killing dozens of alleged militants.

New Delhi regularly blames Islamabad for arming and training rebels before sending them across the border into Indian-administered Kashmir. Pakistan denies the charges.