NEW DELHI: A grandmother who slipped across one of the world's most guarded frontiers and a new border post being built in response could have been the catalysts for the worst flare-up between the armies of India and Pakistan since 2003, a newspaper report and a resident said.

At least four soldiers, two from each side, have been killed in clashes since last Sunday in disputed Kashmir, where the nuclear-armed states are separated by a Line of Control (LoC) set up in 1948.

Taken together, it is the worst violation of a nine-year ceasefire along the 740 kilometre zig-zag line across the mountainous Himalayan region, although exchanges of gun and mortar fire are commonplace. Both armies are said to maintain snipers and special assault teams close to the line.

“It still is an eyeball-to-eyeball confrontation. On some days, people can't step out of the post. If you come out for water, there is firing,” said Gurmeet Kanwal, a retired Indian army brigadier who has commanded troops on the line.

The two countries have fought three wars since they gained independence from colonial Britain in 1947, two of them over Kashmir, a region they both claim. On at least two other occasions, they have come close to war.

While the two countries share a formal international border to the south, all the way down to the Arabian Sea, the Kashmir ceasefire line is where the armies are on a knife-edge.

Strung out on remote outposts in snow-capped mountains and over deep valleys, in some places the soldiers are as little as 50 metres apart.

In other areas, there is a strip of land between the actual line and a barbed wire fence constructed by India.

The fighting can be controlled but merciless. Every violation of the ceasefire by one side is replied in kind by the other. If a soldier is killed on one side, almost certainly one will be killed on the other within days.

The roots of this week's clashes could be traced to Reshma Bi, a 70-year-old woman who slipped across from Charonda village in India-administered Kashmir's Uri district to the Pakistani side in September, to join her sons and grandchildren, India's The Hindu newspaper reported.

Indian authorities, worried about the vulnerability of the LoC, began building a new bunker near the frontier to house additional troops, Reyaz Ahmad, a resident of Charonda, told Reuters. He said it happened soon after Reshma Bi's flight, but could not say if the two incidents were related.

Subsequently, Pakistani troops began making announcements by loudspeaker asking the Indians not to proceed with the construction.

“There were announcements from the Pakistani side for several days to stop the work,” Ahmad said in a telephone conversation. While the Pakistani position was that any construction within 500 metres of the LoC was prohibited under the terms of the ceasefire agreement, India proceeded on the grounds that the bunker was facing the village and not the LoC, and so should not be a problem.

“We can build defences on our side of the LoC. They are doing the same thing that they did when we were trying to construct the fence,” said a defence official in New Delhi who asked not to be named due to the sensitivity of the issue.

Tit-for-tat

Soon after the loudspeaker warnings, firing erupted in the area in October in which India said three villagers were killed, blaming the deaths on Pakistan.

Since then tensions have been running high and, last Sunday, a Pakistani soldier was killed in what Islamabad said was a cross-border raid mounted by the Indians. The Indian army denied any of its troops breached the control line, but said there had been an exchange of fire.

Two days later, further south along the LoC in the Mendhar district, two Indian soldiers were reported killed in a thick forest after what Indian officials said was a deep incursion into their territory by Pakistani forces.

Indian Brigadier Jayant K. Tiwari, the local commanding officer, said the head of one of the bodies had been “badly severed”.

On Thursday, hostilities erupted again in another part of the ceasefire line, and this time Pakistan said one of its soldiers had been killed.

“It is a live LoC. It's not marked by boundary pillars. So this is par for the course,” said Kanwal, the retired Indian officer.

In Pakistan, a retired general who has also served on the LoC, said the fighting would not escalate.

“There will be talks on the hotline between the two sides. They will resolve this,” the retired general said.

“It is not something in the scheme of HQ (headquarters), it is a lower level skirmish.”

Nevertheless, clashes have been rising along the LoC in Kashmir since the November 2008 attacks in Mumbai by militants from Pakistan, which led to a deep chill in ties between the two countries.

Last year, there were 117 violations of the ceasefire, nearly double the previous year's 61 incidents and up from 57 in 2010, according to Indian government figures.

Most have taken place in the southern stretch of the LoC, which India says is the most-used route for infiltration of militants from Pakistan into its side of Kashmir.

"There's been an increase in ceasefire violations. There been an increase in infiltration attempts. That is a fact. And that is something that we are dealing with, both ourselves and with the Pakistani authorities," Shivshankar Menon, India's national security adviser, told reporters on Thursday.

Pakistan denies it is helping push militants across and Foreign Minister Hina Rabbani Khar said this week that her country was committed to the ceasefire in Kashmir.

With tensions rising in recent days, villagers on the Pakistani side have also reported an increase in military activity.

"I've seen big movements of army in small and big vehicles since yesterday," said Naveed Chaudhry in the Kotli district of Pakistani-administered Kashmir. "It is unusual and we are worried what is going to happen."

But away from the frontline, top officials in the two countries have sought to contain the fallout from the clashes on the Kashmir frontline.

"Pakistan has its hands full with a full-blown insurgency inside its borders. It doesn't suit Pakistani interests at all to raise the temperature along the LoC," said Senator Mushahid Hussain, who is also a member of parliament's committee on national security.

A top Indian national security official also said the trouble at the frontier would be contained and would not drag down the fragile relationship.

"This is not the first time this has happened and not the sum total of our relations. It is Pakistan we are dealing with, give them some time," said the official, who asked not to be named.