India's army has said five of its soldiers were killed when Pakistani troops opened fire at a post near the ceasefire line in the disputed Himalayan region of Kashmir today.
The incident could threaten recent overtures for peace talks to resume between the nuclear-armed rivals.
The military called the attack a "gross violation" of a 2003 ceasefire in Kashmir between India and Pakistan. There were no other details and no immediate comment from Pakistan.
While the ceasefire has largely held for the last decade, such sporadic violations are not uncommon. Each accuses the other of initiating the fighting by firing mortars or gunshots across the line of control.
The two countries have fought three major wars since they achieved independence from British India in 1947, two of them over Kashmir, which is claimed in its entirety by both but divided between them.
Pakistan's newly elected Prime Minister Nawaz Sharif has been indicating he is open to restarting peace talks.
Omar Abdullah, the top elected official of India's Jammu and Kashmir state, said in a tweet that such violent incidents "don't help efforts to normalise or even improve relations" and may even call the recent Pakistan peace overtures into question.
While the two nations remain rivals, relations between them have improved dramatically since the most recent low point in the aftermath of the 2008 Mumbai siege, in which 10 Pakistani gunmen killed 166 people and effectively shut down the city for days. India claims the terrorists had ties to Pakistani intelligence officials - an accusation Islamabad denies.
Signs of their improving ties include new visa rules announced last December designed to make cross-border travel easier. The two countries have also been taking steps to improve cross-border trade.