Nuclear war fears explode as India orders Pakistanis to leave after tourist massacre

has told Pakistani nationals they have 72 hours to leave the country after an attack killed 26 tourists in Indian-administered Kashmir as tensions mount between the two nuclear-armed countries. Indian Prime Minister Narendra Modi vowed to "identify, track and punish every terrorist and their backers" following the militant attack near Pahalgam in the disputed region.

"We will pursue them to the ends of the earth," he warned. has told all Pakistani nationals in the country they must leave by Sunday (April 27) as the country's Foreign Secretary Vikram Misri accused the leaders of Pakistan of sponsoring "cross-border terrorism". Pakistan's Defence Minister Khawaja Asif has told Al Jazeera that the Islamabad government suspects "very strongly" that the attack was a "false flag operation".

also announced other measures against , including reducing the number of diplomatic staff, closing the only functional land border crossing between the nations and suspending a key water-sharing treaty.

responded by cancelling all visas issued to Indian nationals, closing its airspace to Indian flights and suspending all trade with .

The Indian government said the attack had "cross-border" links to , without publicly producing any evidence to support that claim.

has denied any connection to the attack, which was claimed by a previously unknown militant group calling itself the Kashmir Resistance.

Islamabad warned any suspension of water supplies would be considered an "act of war".

It warned any move to alter the Indus Waters Treaty would be met with "full force" from .

The agreement allows for sharing the water of a river system that is key for both countries, particularly for 's agriculture.

It has survived two wars between the countries, in 1965 and 1971, and a major border skirmish in 1999.

Tuesday's attack shocked and outraged Indians.

People in Kashmir took part in street protests and candlelight marches in protest against the killings and in New Delhi, there were protests outside the Pakistani embassy.

While in dozens of demonstrators rallied in some cities, including outside the Indian High Commission in Islamabad, against India's suspension of the water-sharing treaty, demanding their government to retaliate.

has urged its citizens not to travel to Pakistan and urged those in the country to return.