A car bomb has killed 44 policemen in disputed Kashmir, prompting India to demand Pakistan act against militants using its territory, a claim Islamabad denies.
A suicide bomber has rammed a car into a bus carrying Indian paramilitary police in Kashmir, killing 44 of them in the deadliest attack in decades on security forces in the disputed region, raising tensions with arch foe Pakistan.
The Pakistan-based Islamist militant group Jaish-e-Mohammad (JeM) claimed responsibility for the attack.
The Indian government accused Pakistan of letting militant groups operate from its soil and called on it to take action.
Islamabad said it rejected the suggestion it was linked to Thursday's attack.
Kashmir is a Muslim-majority region at the heart of decades of hostility between India and Pakistan. The neighbours both rule parts of the region while claiming the entire territory as theirs.
The explosion targeting a convoy of the Central Reserve Police Force (CRPF) was heard from several kilometres away, according to witnesses.
Mohammad Yunis, a journalist who reached the site minutes later, told Reuters he saw blood and body parts scattered along a 100-metre stretch of the main highway running through the Indian state of Jammu and Kashmir.
"We demand that Pakistan stop supporting terrorists and terror groups operating from their territory and dismantle the infrastructure operated by terrorist outfits to launch attacks in other countries," the Indian foreign ministry said in a statement, hours after the attack.
Pakistan's Ministry of Foreign Affairs called the attack a matter of "grave concern". But in a brief statement early on Friday it added, "We strongly reject any insinuation by elements in the Indian government and media circles that seek to link the attack to the State of Pakistan without investigations."
Islamabad has previously denied New Delhi's accusations that it gives material help to the militants fighting Indian rule in Muslim-majority Kashmir. It says it gives only moral and diplomatic support to the Kashmiri people in their struggle for self-determination.
The White House urged Pakistan in a statement "to end immediately the support and safe haven provided to all terrorist groups operating on its soil". It said the attack strengthens US resolve to step up counter-terrorism cooperation with India.
Television images showed a mangled car amid rubble and snow around the site.
The death toll stood at 44, a senior police official said.
The Central Reserve Force Police is a paramilitary organisation that is working with the Indian military to quell the 30-year insurgency in Kashmir.
"I strongly condemn this dastardly attack. The sacrifices of our brave security personnel shall not go in vain," Prime Minister Narendra Modi said in a tweet.
Arun Jaitley, a senior minister in Modi's cabinet, said India would retaliate, tweeting that "terrorists will be given unforgettable lesson for their heinous act".