NEW DELHI Secretary of State Condoleezza Rice was due in New Delhi on Wednesday as part of intense U.S. efforts to ease tension between India and Pakistan that has surged over the Mumbai attacks.
The top U.S. military commander was also visiting the nuclear-armed South Asian rivals and India's senior-most diplomat held meetings in Washington in other initiatives.
The 10 Islamist gunmen who killed 183 people in a three-day rampage in India's financial capital last week were from a Pakistani militant group, investigators said.
India has long said Pakistan is unable or unwilling to act against groups on its soil that launch such strikes and the attacks threatened to unravel improving ties between the adversaries, who have fought three wars since independence from Britain in 1947.
Islamabad has denied involvement and condemned the Mumbai attacks.
India's Foreign Minister Pranab Mukherjee said military action was not being considered but later warned a peace process begun in 2004 was at risk if Pakistan did not act decisively.
"It has vitiated the atmosphere," Mukherjee said of the attacks in an interview to NDTV television. "While we have no intention of not carrying on with the peace process, when people's sentiments are affected it creates an atmosphere not to carry on business as usual, it has some impact."
The deterioration could also put U.S. counterterrorism efforts in the region at risk -- Islamabad has said the tensions may force it to shift troops from operations against al Qaeda militants on the Afghanistan border to the frontier with India.
Rice cut short a European tour to meet Indian Prime Minister Manmohan Singh, who is under election-year pressure to craft a muscular response to opposition criticism his ruling Congress party is weak on security.
Navy Admiral Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, would also visit the region starting on Wednesday, officials said. They declined to give specific details.
"The chairman intends to meet with civilian and military leaders of both nations to encourage a cooperative approach to regional security concerns in the wake of the Mumbai attacks," Navy Capt. John Kirby, a spokesman for Mullen, said by e-mail.
"He believes the attacks, which also killed Americans, point to a growing sophistication of extremist groups that threaten the entire region."
India's Foreign Secretary Shivshankar Menon met Deputy Secretary of State John Negroponte and other officials in Washington on Tuesday.
India and Pakistan were on the brink of a fourth war in 2002, just a few years after both demonstrated nuclear weapons capabilities, following an attack on India's parliament by Islamist militants.
They pulled back after frantic diplomacy by the United States and other allies.
On Monday, New Delhi renewed a long-standing demand for about 20 fugitives it believes are hiding in Pakistan, a Muslim nation carved from Hindu-majority India in 1947.
Officials said the list includes Dawood Ibrahim, a Mumbai underworld boss blamed for 1993 bombings in Mumbai that killed 250, and Maulana Masood Azhar, a Pakistani Muslim cleric freed from jail in India in exchange for passengers on a hijacked jet.
Pakistan has said it is willing to act against Islamist groups if given proof of their involvement in the Mumbai attacks and offered a joint probe.
"We don't want to do anything in haste. We don't want to do anything that fuels confrontation," Pakistani Foreign Minister Shah Mehmood Qureshi told reporters after an all-party meeting on relations with India. "We want to defuse the situation."
Islamabad has said it is battling the same kind of enemy at home. In the past year, hundreds of people have been killed in militant attacks across Pakistan, including a suicide bombing which destroyed the Marriott hotel in Islamabad.
"The state of Pakistan is no way responsible," Pakistani President Asif Ali Zardari told CNN's "Larry King Live" program.
Mumbai's police chief Hasan Gafoor said the attackers had trained for a year or more in commando tactics. Azam Amir Kasav, the only gunmen of the 10 not killed by commandos, told investigators he is a Pakistani citizen from Punjab, Gafoor said.
But Zardari said India had provided no proof the gunman was Pakistani.
Investigators have said a former Pakistani army officer led the training, organised by the Pakistani Lashkar-e-Taiba group, that was also blamed for the 2001 attack on India's parliament. Ibrahim is said to be one of its financial backers.
U.S. officials say the attacks bear the hallmarks of operations by groups like Lashkar-e-Taiba and Jaish-e-Mohammed, which have fought Indian rule in Kashmir.
Many Indians have expressed anger at apparent intelligence lapses and a slow security reaction to the attacks against Mumbai's two best-known luxury hotels and other landmarks in the city of 18 million.