Relations between nuclear-armed neighbours India and Pakistan have plummeted to fresh lows after the killing of 26 people in a tourist hotspot.
India blamed Pakistan for supporting the militants behind the attack but provided no public evidence for the claim, prompting a diplomatic stoush.
But India's move to temporarily suspend a decades-old water deal sparked the biggest reaction from Islamabad, saying any such move would constitute an "act of war".
There has always been tension between the two countries, but here's how India and Pakistan went from unhappy neighbours to threatening war over water.
What is Kashmir?
After Britain partitioned the subcontinent in 1947, Kashmir was expected to go to Pakistan, as other Muslim-majority regions did.
Its Hindu ruler wanted to stay independent but, faced with an invasion by Muslim tribesmen from Pakistan, acceded to India in October 1947 in return for help against the attackers.
The area was divided among Hindu-majority India and Muslim-majority Pakistan.
India governs the Kashmir Valley, Jammu and Ladakh.
Pakistan controls Azad Kashmir ("Free Kashmir") and the northern areas, while China holds Aksai Chin.
Both Pakistan and India claim the Kashmir area in its entirety, but partially control only some of it.
[MAP]Kashmir has been at the centre of two wars fought between India and Pakistan.
A third war in 1971 saw the creation of Bangladesh.
A Muslim insurgency has fought Indian rule in the region for decades, pushing for a united region under Pakistani rule or an independent country.
Tens of thousands of people have died in the bloodshed.
India has accused Pakistan of arming and training militants, something Islamabad has denied.
Pakistan says it offers only moral and diplomatic support.
In 2019, the Indian government removed the region's semi-autonomous status and took Kashmir under the control of New Delhi, angering Pakistan.
What happened in Kashmir?
Armed militants killed 26 people in the tourist hotspot of Baisaran valley near Pahalgam in the Himalayas on Tuesday.
It was the biggest attack on civilians in India since the Mumbai terror attacks in 2008.
India's Prime Minister Narendra Modi said on Thursday his country would pursue those responsible "to the ends of the Earth".
Local police described it as a "terror attack" and India accused Pakistan of supporting the militants behind the violence.
Pakistan denied it had anything to do with the attack.
The accusation has sparked a diplomatic downgrade between the two countries to the lowest level since 2019.
Senior officials have been expelled from both New Delhi and Islamabad, visas for respective nationals have been cancelled and the main land border between the two countries has shut.
Pakistan has paused trade with India and shut its airspace to Indian airlines.
India also announced it had suspended the Indus Waters Treaty (IWT).
[THE WORLD IV]What is the Indus Waters Treaty?
The IWT has stood since 1960 and outlines how water that comes from the Indus River system can be used by India and Pakistan.
The deal was brokered by the World Bank and has survived the three wars India and Pakistan have fought.
Under the agreement, India has control over the eastern rivers of Ravi, Sutlej and Beas.
Pakistan controls the western rivers of Jhelum, Chenab and Indus that flow through the Kashmir region.
Pakistan is downstream in the river system.
The water it provides accounts for 80 per cent of Pakistan's irrigated agriculture and its hydropower plants.
Islamabad has long accused India of diverting water upstream by building barrages and dams, something India denies.
Pakistan has asked a neutral expert in an arbitration court to intervene in two Indian hydropower projects in recent years.
That has prompted India to accuse Pakistan of dragging out the complaints process.
India has also sought modifications to the treaty to get around such delays.
What does the IWT's suspension mean?
A statement from Pakistan Prime Minister Shehbaz Sharif's office said the deal contained no clause that allowed for a unilateral suspension.
Regardless, the suspension was not expected to immediately affect the flow of water into Pakistan, because India did not have enough storage to hold it.
However, it is likely to cause some uncertainty within Pakistan's agricultural sector.
Indian officials say New Delhi's decision means it can stop sharing information on water releases from dams and on flooding.
They also say that India will not be obliged to to release minimum amounts of water during lean season.
Ghasharib Shoukat, the head of product at Pakistan Agriculture Research, called the treaty the backbone of the country's agriculture sector.
"It puts our agricultural future on shaky ground. If water flows become erratic, the entire system takes a hit — especially irrigation-dependent crops such as wheat, rice, and sugarcane," Mr Shoukat told Reuters.
"Yields could drop. Costs could rise. Food prices would likely spike. And small-scale farmers, who already operate on thin margins, would bear the brunt of it."
Khalid Hussain Baath, chairman of a national farmers' union in Pakistan, painted the move as an act of belligerence.
"This is a true war," Mr Baath told Reuters from Lahore.
"We already have a water shortage because of climate change. Low rainfall this year, and limited snow means that the water level is already 20-25 per cent lower than last year."
ABC/wires
