NEW DELHI — India vowed Thursday to cut back on water flowing through its rivers to arid Pakistan, a threat it has made before but now seems more determined to carry out in the wake of a suicide bomb attack last week that India has blamed on Pakistan.
Nitin Gadkari, India’s transport minister, said in a Twitter message that “Our Govt. has decided to stop our share of water which used to flow to Pakistan. We will divert water from Eastern rivers and supply it to our people in Jammu and Kashmir and Punjab.”
Some analysts said this was the strongest threat India has made yet since the attack in which a suicide bomber killed more than 40 Indian troops in the disputed region of Kashmir.
A full-blown water war could be catastrophic to the hundreds of millions of people in India and Pakistan who depend on river water. But this latest threat was not accompanied by details on when or how India might act to divert more water from Pakistan downstream or how large, in reality, such diversions would be.
Under a longstanding treaty governing the use of the Indus River and its tributaries, Pakistan still controls most of the water and India has not challenged that.
India has been struggling to find a way to punish Pakistan for the attack last week. The bomber was a young man who grew up in the India-controlled part of Kashmir. He rammed a car full of explosives into an Indian convoy, ripping apart a bus packed with paramilitary troops.
But India was quick to accuse Pakistan, its neighbor and long time bitter rival, of helping the bomber pull off his deadly mission.
For decades, Pakistan and India have been locked in a violent dispute over Kashmir, a mountainous territory that both nations claim. Western intelligence officials have said that Pakistani security services allow anti-India militants to operate in Pakistan and that some of these militant groups provide material support and expertise, like bomb-making know-how, to insurgents in the Indian-controlled parts of Kashmir.
But Pakistan no longer runs large militant training camps as it had in the 1990s and early 2000s, these officials said.
Each day since the attack, India and Pakistan have traded barbs, threatened and insulted each other and, at the same time, tried to carefully woo other countries to their sides. India is eager to isolate Pakistan, but Pakistan has powerful friends in China and Saudi Arabia, both major investors.
Though this latest attack seemed to strike a nerve in India, with many people hungry for revenge, India has few good military options. Both India and Pakistan field nuclear arsenals and thousands of troops on the border. Even the most jingoistic members of India’s military elite are wary of escalating tensions.
So the Indian government has looked for other ways to hit back or, in the views of some of its critics, appear as though it is hitting back. This is hardly the first time it has threatened to choke Pakistan’s water supply.
In 2016, after militants attacked an Indian army base near the town of Uri, Prime Minister Narendra Modi said “blood and water can’t flow together” and his government threatened to do the same thing. Instead, the Indian military staged what it called surgical strikes against targets just across the border in Pakistan.
This time around, India seems more serious about using water as punishment. Under the Indus Water Treaty, a World Bank-brokered agreement that goes back decades, India and Pakistan divided the rights to the enormous Indus River and its tributaries that wind across the subcontinent.
Both sides have grumbled over certain provisions and both rely heavily on the water flows for hydropower and agriculture.
On Thursday, after Mr. Gadkari’s threat to reduce the flow of water from the Indus’s eastern tributaries into Pakistan, Indian media reported that officials in that same ministry clarified that this was a longstanding policy.
Even before the attack, Indian officials said that water allocated to India under the treaty was flowing to Pakistan and that it planned to use those flows for new hydropower projects and farms.
Brahma Chellaney, a professor at Center for Policy Research in New Delhi and an expert on the India-Pakistan water treaty, said that for years India has struggled to harness waters from the rivers that it controls.
“This statement by the Indian government is an attempt by them to show to the country that the government appears to be doing something,” Mr. Chellaney said. “When in actual terms they have done nothing. This is more of a rhetorical statement being used to play to the popular anti-Pakistan sentiment.”
Pakistan has yet to officially respond to the water threat. But on Thursday, Pakistan once again denied any role in the suicide bombing, saying it was “not involved in any way, means or form in the said incident.”
The statement from the office of Prime Minister Imran Khan added, “India also needs deep introspection” to realize “why people of IOK have lost fear of death.”
IOK is shorthand for what Pakistan calls India Occupied Kashmir and the statement was alluding to the legions of young men from villages across India-controlled Kashmir who have joined the militants or taken part in dangerous street demonstrations to protest Indian control. The response to such demonstrations is often heavy handed with Indian security forces firing pellet guns and live ammunition into crowds.
Arif Rafiq, a political analyst at the Middle East Institute in Washington, said India’s threats are driven by national elections expected in the coming months.
Mr. Modi’s government needs to look tough, he said, and is signaling “that it can leverage its upper riparian location to coerce Pakistan.”
“While I don’t see any imminent threat to Pakistan,” Mr. Rafiq added, “we may be getting a glimpse of the future of conflict in South Asia. The region is water-stressed. Water may be emerging as a weapon of war.”