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A senior American diplomat ended a two-day visit to India and Pakistan on Thursday aimed at reducing the military standoff between the nuclear-armed rivals but reported little sign of progress, saying, “This is not the work of one trip.”

The mission by Christina Rocca, assistant secretary of state for South Asia, came two days after an attack in the Indian state of Jammu and Kashmir that killed 34 people, mostly women and children, in a passenger bus and at an Indian army barracks.

India quickly blamed Pakistan for sheltering the Islamic militants who it said were behind the attack, and Pakistan condemned the killings almost immediately.

But it was the kind of incident that diplomats fear could open a war between the two nations, which have a million troops facing each other on a hair trigger along their 1,800-mile border.

The risks of a conflict were also highlighted by a recent report that Pakistan’s military might have prepared its nuclear weapons for use during the last round of skirmishing between the two countries in Kashmir’s icy mountains in 1999.

“We’re very worried about the continued mobilization of two major armies facing each other at close proximity and the possibility of a spark that could lead to an unintended conflict,” Rocca said in New Delhi early Thursday before leaving for Islamabad.

In Pakistan, she met with President Pervez Musharraf to, as she put it, “explore ways with which India and Pakistan can move away from the dangerous confrontation that has characterized their relations” since India mobilized troops after it blamed Pakistan-based militants for a suicide attack on its parliament in December.

The attack Tuesday placed more pressure on Rocca’s mission, as well as on India’s government for possible retaliation. In a sign of just how difficult her discussions in the two countries have been, the diplomat on Thursday refused even to describe the substance of her talks.

Indian officials expressed hopes that Rocca would use America’s full influence to get Musharraf to end what they charge is Pakistan’s continued support for extremist Islamic groups waging a holy war to drive India from Kashmir, their only Muslim-majority state.

In January, Musharraf banned several militant Islamic groups, including some that have sent fighters across the border into the Indian part of Kashmir.

Diplomats say that most of these groups continue to function, however, often simply changing their names.

On Wednesday, Indian leaders vowed to take tough, punitive action in response to Tuesday’s attacks.

Defense Minister George Fernandes said that the three assailants, who were shot dead, were Pakistanis and that the attacks reflected “the frustration of the Pakistani leadership.”

“It is a situation which calls for punishment,” Fernandes said during a visit to the site of the attack near the northern city of Jammu.

“We cannot have this kind of terrorism go unpunished. What that punishment should be is something that needs to be deliberated upon.”

Speaking in parliament, Indian Prime Minister Atal Behari Vajpayee called the attack a “massacre of innocents” and said his country would have to retaliate.