India has threatened before, in other moments of rising tensions, to pull out of the Indus Waters Treaty, which both countries signed in 1960. If India follows through this time, it could restrict the flow of water that is used for most of Pakistan’s crop irrigation and human consumption. Agriculture represents one-fourth of the country’s economy.

Indian and Pakistani soldiers have exchanged heavy volleys of shells and gunfire across their frontier in Kashmir, killing at least five civilians in a growing military standoff.