India blamed Pakistan on Wednesday for a militant attack that killed 26 people in Indian-held Kashmir, downgrading diplomatic ties and suspending a crucial water-sharing treaty that has withstood two wars between the nuclear-armed rivals.

The spray of gunfire at tourists Tuesday in a scenic, mountain-ringed valley was the worst assault in years targeting civilians in the restive region that is claimed by both countries. The unidentified gunmen also wounded 17 other people.

India’s foreign secretary, Vikram Misri, announced the diplomatic moves against Pakistan at a news conference in New Delhi late Wednesday, saying a special cabinet meeting called by Prime Minister Narendra Modi decided that the attack had “cross-border” links to Pakistan. However, the government provided no evidence of this publicly.

Pakistan said it would respond more fully to India’s actions on Thursday, but in the meantime Pakistani Defense Minister Khawaja Mohammad said that India was using “an unfortunate incident of terrorism” as a pretext to jettison a treaty it has long been trying to evade.

India describes militancy in Kashmir as Pakistan-backed terrorism. Pakistan denies this, and many Muslim Kashmiris consider the militants to be part of a home-grown freedom struggle.