SRINAGAR, India – Three Indian soldiers were killed Tuesday along the highly militarized de facto border that divides the disputed region of Kashmir between India and Pakistan, army officials said.

Army spokesman Col. Rajesh Kalia said the attackers also mutilated the body of one soldier in Machil sector in Indian-controlled Kashmir.

“Retribution will be heavy for this cowardly act,” he said.

Kalia did not specify if the attack was carried out by Pakistani soldiers or rebels fighting since 1989 against Indian rule in the region.

In the past, the Indian army has blamed a combination of the Pakistani army’s border action team and militants for carrying out operations along the Line of Control.

Following the attack, heavy cross-border firing and shelling began at several posts in Machil sector.

An Indian army officer, speaking on condition of anonymity in keeping with military rules, said the three soldiers were ambushed by a team of attackers who came from the Pakistani side.

Pakistan’s army insisted that it only returned fire after coming under attack near the Line of Control.

Also Tuesday, Pakistan’s Foreign Ministry lodged a protest with India over continued cease-fire violations in Kashmir.

India and Pakistan have regularly traded fire in recent months in the Himalayan region, which is claimed by both in its entirety.

Tensions have been running high since militants attacked an Indian army base in Kashmir in September. India blamed Pakistan for supporting the militants and said it carried out “surgical strikes” against militants in the Pakistan-controlled part of Kashmir.

Pakistan dismissed the claim and called on India to produce evidence to back it up.

Both sides accuse the other of initiating the firing.

Two of the three wars between India and Pakistan since 1947 have been fought over their competing claims to Kashmir.

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Associated Press writer Munir Ahmed in Islamabad, Pakistan, contributed to this report.