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.

Relations between India and Pakistan are cratering following a deadly militant attack in Indian-administered Kashmir that has sparked tit-for-tat reprisals and raised fears of another military escalation between the nuclear-armed rivals.

Indian officials said the army had a brief exchange of fire with Pakistani soldiers along their highly militarized frontier in the Himalayan region of Kashmir, as the nuclear-armed rivals ramped up ti