NEW DELHI — A deadly attack on tourists in Indian-controlled Kashmir has again moved India and Pakistan closer to war as the two rivals downgraded diplomatic and trade ties, closed the main border crossing and revoked visas for each other’s nationals.

India and Pakistan have intensified their hostilities over the hotly contested Kashmir region following a massacre of 26 mostly Indian tourists, which New Delhi linked to Pakistan.

Troops from Pakistan and India have exchanged fire in the disputed valley of Kashmir, officials in Islamabad said on Friday, as tensions between the rival nuclear powers escalate following a deadly terrorism attack in the region.