The bus service, due to start on April 7, is the first substantive result from just over a year of talks between South Asia's nuclear rivals.

Now it has to run the gauntlet of potential attacks by irreconciled militant groups as it crosses a mountain road through one of the world's most dangerous flashpoints.

The accord struck on Wednesday during Indian Foreign Minister Natwar Singh's visit to Islamabad prompted relief that a dip in relations over Pakistan objections to a dam being built by India had not stopped both sides advancing the peace process.

But, there were apprehensions too.

"It's very easy to start a bus service... but it is a potential minefield in terms of sustainability and security," said Riffat Hussein, a defence analyst at Quaid-e-Azam University in Islamabad, saying both the Indian and Pakistani security forces will have to safeguard the route.

Two Kashmiri guerrilla groups based on the Pakistan side of Kashmir ceasefire line declared their opposition on Thursday, but neither issued an outright threat.

Not just a bus journey

It is tantamount to betraying the blood of the mujahideen of Kashmir," said a spokesman for Jaish-e-Mohammad, whose leader Masood Azhar was freed from an Indian prison in exchange for hostages of a hijacked Indian airliner in 2000.

"Our next line of action will be in line with the wishes of the majority of Kashmiris," he said without elaboration.

Syed Salahuddin, the commander of Hizbul Mujahideen, another pro-Pakistan Kashmiri militant group took a similar line.

Maria Sultan, a visiting analyst from Bradford Disarmament Research Centre in Britain said attacking a peace bus may prove to be counter-productive

"There are fringe elements who are extremists, but I don't think they would attack a bus service that vindicates their claim that Kashmir is something beyond borders," she said.

Najam Sethi, editor of a Pakistan newspaper, the Daily Times, said the militants are isolated and will ultimately fail "because for the first time the establishments in Pakistan and India and the people on both sides want it to succeed".

Bus service is a potential minefield in terms of sustainability and security

"It's not just a bus journey. It's going to unite shattered homes and create trade and commerce, giving Kashmiris on both sides a reason to support the peace process," Sethi told Reuters.

Indian media was more effusive than most Pakistani newspapers in hailing the Kashmir bus initiative.

Peace Communities

The move was accompanied by statements of good intentions on several other fronts, notably India's decision to "look at" proposals for a gas pipeline from Iran to India, via Pakistan, the opening of other transport routes and a commitment to finalise terms for notify each other before missile tests.

"Win-Win for both: India, Pak rev up on road to peace," the Times of India trumpeted on its front page on Thursday.

Pakistan's English-language daily, The Nation, had a different view, more in keeping with its government's desire to move swiftly beyond confidence building measures and negotiate a settlement to Kashmir -- the cause of two of three wars fought by the neighbours since their independence and partition in 1947.

"Although welcome, the decision could hardly be called a breakthrough," said The Nation's editorial. "The bus service would touch only a fringe of Kashmiris' problems."

India says it will not entertain any changes to the existing frontier, the so-called Line of Control drawn after the 1947/48 war and validated in the 1972 Shimla accord.

But in agreeing to the bus service, New Delhi conceded that Kashmiris making the journey will need permits rather than passports, which Pakistan said could have been construed as tacit recognition of the LoC as an international border.

This soft border approach to the Kashmir, according to Sultan, could allow "peace communities" to flourish in a region scarred by a 15-year insurgency that has killed 45,000 people in Indian-held Kashmir.

"This normalisation could create space for the opening of negotiations on the issue of Kashmir... and introduce a situation where both sides can no longer maintain their current positions."