ISLAMABAD U.S. Secretary of State Condoleezza Rice said on Thursday Pakistan had given assurances of its commitment to root out terrorism and round up anyone connected to last week's attack in the Indian city of Mumbai.
Rice, on a trip aimed at curbing tension between nuclear-armed India and Pakistan, said the Mumbai attack showed a level of sophistication unseen in the region and urgent action was needed to get the perpetrators and prevent more attacks.
But she played down fear of a military response by India, saying the global struggle against terrorism needed cooperation.
India and U.S. officials have blamed groups based on Pakistani territory for the attack, but no accusations have been leveled at the Pakistani state or its agencies.
Pakistan has condemned the assault, denied any involvement by state agencies and vowed to help the Indian investigation, but it wants proof of Pakistani involvement.
In a delicate balancing act, Rice met Indian leaders on Wednesday in New Delhi, where she called for restraint. Rice said she had reasonable and responsible discussions in both capitals.
The assault on India's commercial capital killed 171 people, including six Americans.
"This was a terrible attack. It was a sophisticated attack, a level of sophistication that we haven't seen here on the subcontinent before," Rice told a news conference at a military airfield before departing.
"That means that there is urgency to getting to the bottom of it. There is urgency to bringing the perpetrators to justice and there is urgency to ... disrupt and prevent further attacks."
Her talks in Islamabad included the importance of Pakistan dealing with anyone who may use its territory for attacks, even if they were "non-state actors", she said, adding everyone wanted to prevent more attacks.
"Pakistan, the Pakistani leadership, understands the importance of doing that, particularly in rooting out terrorism and rounding up whoever perpetrated this attack," she said.
President Asif Ali Zardari, who had been trying to push forward a peace process with India, told Rice he had asked India to see this as a chance to work together rather than be at odds, saying: "I intend to do everything in my power".
"The government will not only assist in investigations but also take strong action against any Pakistani elements found involved in the attack," a statement quoted Zardari as saying.
"Pakistan is determined to ensure that its territory is not used for any act of terrorism," he said.
The prime suspect for the Mumbai slaughter is Lashkar-e-Taiba, a jihadi group fighting Indian rule in disputed Kashmir that also has al Qaeda links, and which analysts say has had ties with Pakistani intelligence in the past.
Before meeting Zardari and Prime Minister Yousaf Raza Gilani, the leaders of Pakistan's eight-month-old civilian government, Rice met army chief General Ashfaq Kayani at army headquarters in Rawalpindi, adjacent to Islamabad.
Traffic was blocked and no people were in sight apart from security personnel lining the roads as Rice's motorcade passed through two cities living under threat of militant attacks.
How much leverage the United States, particularly the outgoing Bush administration, has over Pakistan is debatable. Withholding financial or military support could add to instability in the Muslim state.
The country is in the midst of a fragile transition to democracy after more than eight years of rule under former army chief Pervez Musharraf, and analysts say the new government does not have full control over the army's affairs.
A confrontation between the South Asian rivals would undercut efforts to bring stability to Afghanistan and defeat al Qaeda.
Pakistani security officials have said they could feel compelled to abandon the campaign against militancy and take forces away from the Afghan border, where they are fighting al Qaeda and the Taliban, and move them to the Indian border if tension increases.
Speaking in New Delhi, Rice made clear that India should show restraint to avoid fuelling tension between the neighbors who have fought three wars since independence in 1947. She said in Islamabad she had had no talks about military action.
"The issue is how to respond in a way that is effective and the most effective way to respond is international cooperation," she said. "It doesn't help to do something that might worsen the problem and have unintended consequences."
Chairman of the U.S. Joint Chiefs of Staff Admiral Mike Mullen visited Islamabad a day before Rice and then went to India. The two met for breakfast in New Delhi to compare notes.
Mullen encouraged Pakistan to act against jihadi groups everywhere, not just in regions bordering Afghanistan.
In New Delhi, Mullen "thanked Indian officials for their restraint and their desire to cooperate with Pakistani officials in the pursuit of those responsible for the attacks", the U.S. embassy said in a statement.
While vowing full cooperation with India, Pakistan has indicated it will not accept an Indian demand to hand over 20 wanted men said to be living there.
(Additional reporting by New Delhi and Islamabad bureaux; Writing by Simon Cameron-Moore; Editing by Paul Tait)