"Pakistani troops simply attacked the Indian post, violating the ceasefire and they killed five of our soldiers," a senior army official in Indian-administered Kashmir told AFP on condition of anonymity on Thursday.
Sources in the defense ministry in New Delhi confirmed the Monday night incident, which occurred just days after Pakistan proposed restarting peace talks with India.
The killings took place 200 kilometers (124 miles) south of the state capital, Srinagar.
The picturesque Himalayan territory of Kashmir is divided between India and Pakistan by an UN-monitored de facto border known as the Line of Control (LOC), but is claimed in full by both countries.
Omar Abdullah, the state's chief minister, tweeted about the attack and said: "Was briefed early this morning about news that 5 of our soldiers had been killed on the LOC. My heartfelt condolences to their next of kin."
"These incidents don't help efforts to normalize or even improve relations with Pak & call in to question the Pak Government's recent overtures," he tweeted.
A spokesman for the Pakistan army told AFP he had "no information" about the attack.
More than a dozen armed rebel groups have been fighting Indian forces since 1989 demanding independence for Kashmir or a merger with Pakistan.
India and Pakistan have fought three wars since their independence from Britain in 1947, two of them over Kashmir.
BA/BA