India's Prime Minister Narendra Modi has said that water from India that once flowed across borders will be stopped, days after suspending a key water treaty with arch-rival Pakistan.
New Delhi has blamed Islamabad for backing a deadly attack on tourists on the Indian side of contested Kashmir last month, sparking a series of heated threats and diplomatic tit-for-tat measures.
Pakistan rejects the accusations.
On Tuesday, the Indian armed forces launched "Operation Sindoor," striking nine targets across Pakistan and Pakistan-administered Jammu and Kashmir.
Pakistan's military spokesman said India fired missiles at three locations, warning that Islamabad will respond.
Earlier in his speech, Modi did not mention Islamabad specifically, but the development comes after New Delhi suspended its part of the 65-year-old Indus Waters Treaty, which governs water critical to Pakistan for consumption and agriculture.
"India's water used to go outside, now it will flow for India," Modi said in New Delhi.
"India's water will be stopped for India's interests, and it will be utilised for India."
Pakistan has warned that tampering with its rivers would be considered "an act of war".
But experts also pointed out that India's existing dams do not have the capacity to block or divert water, and can only regulate timings of when it releases flows.
India fires missiles on Bahawalpur in southern Punjab province and targets several parts of Pakistan-administered Kashmir, Pakistani Army confirms.
International pressure has been piled on both New Delhi and Islamabad, who have fought several wars over Kashmir.
"We continue to urge Pakistan and India to work towards a responsible resolution that maintains long-term peace and regional stability in South Asia," US State Department spokeswoman Tammy Bruce told reporters.
'Not natural'
Earlier on Tuesday, Islamabad accused India of altering the flow of the Chenab River, one of three rivers placed under Pakistan's control according to the now suspended treaty.
"We have witnessed changes in the river (Chenab) which are not natural at all," Kazim Pirzada, irrigation minister for Pakistan's Punjab province, told AFP.
Punjab, bordering India and home to nearly half of Pakistan's 240 million citizens, is the country's agricultural heartland, and "the majority impact will be felt in areas which have fewer alternate water routes," Pirzada warned.
"One day the river had normal inflow and the next day it was greatly reduced," Pirzada added.
In Pakistan-administered Kashmir, large quantities of water from India were reportedly released on April 26, according to the Jinnah Institute, a think tank led by a former Pakistani climate change minister.
"This is being done so that we don't get to utilise the water," Pirzada added.
The Indus River is one of Asia's longest, cutting through ultra-sensitive demarcation lines between India and Pakistan in contested Muslim-majority Kashmir — a Himalayan territory both countries claim in full.
Rebels in Indian-run Kashmir have waged an insurgency since 1989, seeking independence or a merger with Pakistan.
India regularly blames its neighbour for backing gunmen behind the insurgency.
Modi had already threatened to use water as a weapon in 2016.
"Blood and water cannot flow together," he said at the time.
