Two officials at Pakistan's High Commission in New Delhi were being expelled for "espionage activities", India's foreign ministry said late Sunday, allegations its nuclear-armed rival called "baseless".
Tensions are already heightened between the neighbouring foes over the Himalayan region of Kashmir, which was split between them in 1947 when they gained independence from Britain.
"The government has declared both these officials persona non grata for indulging in activities incompatible with their status as members of a diplomatic mission," the ministry said in a statement.
The pair had to leave the country "within 24 hours" and Pakistan's charge d'affaires was issued with a "strong protest" over their alleged activities, the ministry said.
Pakistan's foreign ministry said it "strongly rejects the baseless Indian allegations" and called Delhi's action a "clear violation of the Vienna Convention… especially in an already vitiated atmosphere".
Kashmir has become a bigger source of tension in relations between the regional powers after New Delhi last August scrapped the Muslim-majority region's semi-autonomous status and imposed a curfew.
In response, Islamabad at that time said it would recall its ambassador from Delhi and send back the Indian envoy.
Late Sunday, Pakistan summoned India's charge d'affaires to express its "condemnation" of the expulsion order.
India and Pakistan have fought three wars against each other since independence, including two over Kashmir where they have rival claims.
There have also been numerous flare-ups between the two foes, including in February 2019 when they conducted tit-for-tat air strikes.
Rebel groups in Indian-administered Kashmir have battled for decades for the region's independence or its merger with Pakistan, and enjoy broad popular support.
Since 1989 the fighting has left tens of thousands dead, mostly civilians.
India has more than 500,000 troops stationed in Kashmir, where clashes are a common occurrence but last month extended into the regional capital Srinagar. Police said a key rebel leader was killed during the first shootout between Indian government forces and militants to hit the city's centre in two years.
Friction with neighbours
Sunday's expulsion order came after a German court in early May said an Indian national will stand trial there in August accused of spying on Sikh and Kashmiri communities for New Delhi's secret service.
India is also experiencing increased friction with its other neighbours China and Nepal.
India has several disputes with regional superpower China along their 3,500-kilometre (2,175-mile) border.
Hundreds of Indian and Chinese troops are involved in the latest face-off concentrated in India's Ladakh region just opposite Tibet.
New Delhi has turned down US President Donald Trump's offer to mediate that dispute.
The Nepalese government in mid-May drew up a new political map that includes strategically important territory it disputes with India.
The new map followed protests in Nepal after its bigger neighbour inaugurated an 80-kilometre road in Uttarakhand state leading up to a disputed pass.
