SRINAGAR, India — 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.

India announced a raft of measures to downgrade its ties with Pakistan on Wednesday, a day after suspected militants killed 26 men at a tourist destination in Kashmir in the worst attack on civilians in the country in nearly two decades.

The nuclear-armed rivals, which both claim Kashmir and administer separate parts of it, are at a dangerous crossroad after Tuesday’s militant attack, analysts said.