Indian Prime Minister Narendra Modi vowed on Thursday to pursue, track and punish terrorists and their backers in a strong reaction to a deadly militant attack on tourists in Kashmir, where police have identified two of the gunmen as Pakistani.

Pakistan has announced a series of retaliatory diplomatic moves against India and demanded evidence to back up the Indian government’s claims that Islamabad was involved in the Kashmir attack. Suspected rebels killed at least 26 people on Tuesday in the picturesque tourist resort of Pahalgam in the deadliest such attack in a quarter-century in Indian-administered Kashmir.

India says it has revoked all visas issued to Pakistani nationals following a deadly attack by gunmen in Kashmir that killed 26 people, mostly tourists.