The Indian government said Sunday that the two had been detained for "indulging in espionage activities", and given 24 hours to leave the country.

The pair returned to Pakistan via the Wagah border crossing, which has been closed for several weeks because of the coronavirus lockdown, a Pakistan embassy spokesman told AFP.

The move came amid heightened tensions between the arch-rivals foes over the Himalayan region of Kashmir, which was split between them in 1947 when they gained independence from Britain.

Indian media said the two officials -- both working in the embassy visa department -- had been detained Sunday while trying to obtain information on an Indian security establishment.

In a statement late Monday, New Delhi police said one of the men had allegedly posed as the brother of a journalist looking to gain information about Indian Railways, one of the world's largest train networks.

The man was instead trying to procure information about the "movement of (Indian) Army units and hardware" on trains, Delhi Police claimed.

Pakistan had summoned India's charge d'affaires to express its "condemnation" of the expulsion order.

The foreign ministry called the allegations "baseless" and said Delhi's action was a "clear violation" of the Vienna Convention on diplomatic relations.

In response, Pakistan recalled its ambassador from Delhi and sent back the Indian envoy.

Kashmir has become a bigger source of tension between the two powers since India last August scrapped the Muslim-majority region's semi-autonomous status and imposed a major security clampdown.

India and Pakistan have fought two of their three wars since independence over Kashmir.

Shelling and the exchange of fire across their Kashmir demarcation line is a near-daily occurrence, and in February 2019 they conducted tit-for-tat airstrikes.

On Monday in Indian-administered Kashmir, police officer Chandan Kohli told AFP three men were killed after a brief shootout near the de facto border known as the Line of Control (LoC).

A military source told AFP the men were killed just after crossing the LoC.

New Delhi regularly accuses arch-rival Pakistan of arming and sending rebels across the heavily militarised border. Islamabad denies the claims.

Rebel groups in Indian-administered Kashmir have battled for decades for the region's independence or its merger with Pakistan.

Since 1989 the fighting has left tens of thousands dead, mostly civilians.

India has more than 500,000 troops in Kashmir, where clashes are a common occurrence but last month extended into the regional capital Srinagar.