Militants attacked an Indian army brigade headquarters near the de factor border with Pakistan on Sunday, killing 17 soldiers in one of the most deadly attacks in the northern region of Kashmir in a quarter-century-old insurgency.

Four "fidayeen" - or commando-style gunmen willing to fight to the death - were confirmed killed after penetrating the base in Uri near the Line of Control with Pakistan, an Indian army spokesman said.

Indian Prime Minister Narendra Modi strongly condemned what he called the "cowardly terror attack" through twitter.

We strongly condemn the cowardly terror attack in Uri. I assure the nation that those behind this despicable attack will not go unpunished.

— Narendra Modi (@narendramodi) September 18, 2016

"I assure the nation that those behind this despicable attack will not go unpunished," Modi said in a series of Twitter posts.

Television reporters at the scene said the dawn raid had surprised soldiers in their sleep. The attackers set fire to a building before the four were killed in a gunfight that lasted several hours.

An army spokesman confirmed that the number of soldiers killed in the attack had risen to 17, making the toll far worse than a similar raid on an army base in Punjab state in January that India blamed on Pakistan-based militants.

Television footage showed helicopters flying to evacuate the injured as an operation continued to secure the area. Smoke rose from the compound, set in mountainous terrain.

The Defence Ministry put the number of wounded at 35. The raid comes amid heightened tension in India's only Muslim-majority region, which has faced more than two months of protests following the July 8 killing of a popular separatist commander.

At least 78 civilians have been killed and thousands injured in street clashes with the Indian security forces, who have been criticized by human rights groups for using excessive force including shotguns that fire pellets that have blinded people.

Indian-ruled Kashmir is one of the world's most militarized regions, with hundreds of thousands of soldiers, paramilitaries and police deployed to guard the frontier with Pakistan and contain a restive people with strong leanings towards greater autonomy and even independence.

WORST BODY COUNT IN YEARS

The military death toll was one of the worst it has suffered in a single incident during years of conflict in Indian-ruled Kashmir.

Before this attack, 102 people had been killed in separatist attacks in India's part of the Himalayan region this year. Among them were 30 security personnel, 71 militants and one civilian, according to a tally by the New Delhi-based South Asia Terrorism Portal.

Modi recently raised the stakes in the neighbors' decades-old feud by expressing support for separatists in Pakistan's resource-rich Baluchistan province.

Pakistan has, meanwhile, called on the United Nations and the international community to investigate atrocities it alleges have been committed by Indian security forces in Kashmir.

The UN is preparing to hold its annual general assembly in New York, where Kashmir is likely to come onto the agenda amid concerns that India's tough rhetoric could herald a military escalation between the old foes.

Senior Indian journalist and commentator Shekhar Gupta said Pakistan would be "delusional" to think that India would not respond. "This India has moved on from old strategic restraint," he said.

Relations between India and Pakistan have been on edge since the New-Year attack on the Pathankot air force base in Punjab, near the border with Pakistan, that killed seven uniformed men.

India has blamed Pakistan-based militant groups for that and a string of other attacks - including one on Mumbai in 2008 that killed 166 people. After initial progress, an attempt to conduct a joint investigation into the air base attack lost momentum and a tentative peace dialogue has stalled.-Reuters