Pakistan's defence minister said on Monday that a military incursion by neighbouring India was imminent in the aftermath of a deadly militant attack on tourists in Kashmir last week, as tensions rise between the two nuclear-armed nations.

The militant attack killed 26 people and triggered outrage in Hindu-majority India, along with calls for action against Muslim-majority Pakistan.

Asif said Pakistan was on high alert and that it would only use its arsenal of nuclear weapons if "there is a direct threat to our existence".

Following Tuesday's massacre of 26 mostly Indian tourists, hostilities have intensified between India and Pakistan over the hotly contested Kashmir region.

A day after the U.N. appealed for restraint following Tuesday's deadly attack in Indian-administered Kashmir, India reported an exchange of fire across the de facto border in the disputed region.

India said on Monday it had responded to 'unprovoked' small arms firing from Pakistan along the de facto border for the fourth consecutive night, as it deepens its search for militants in the region following last week's deadly attack on tourists in Kashmir.