U.S. calls for India-Pakistan cooperation in investigating Mumbai attacks

"I have said that Pakistan needs to act with resolve and urgency and cooperate fully and transparently," Rice told reporters in New Delhi. "That message has been delivered and will be delivered to Pakistan."

And while the U.S. would not "jump to conclusions" about who was responsible, she said, "this is clearly the kind of terrorism in which Al Qaeda participates."

Even as Rice held talks in India, Navy Adm. Michael G. Mullen, chairman of the U.S. Joint Chiefs of Staff, spent the day meeting with Pakistani government and military officials. Rice is expected to visit Islamabad, the Pakistani capital, on Thursday.

The U.S. Embassy said in a statement that Mullen met with senior officials including President Asif Ali Zardari; the army's chief of staff, Gen. Ashfaq Kayani; and the head of Pakistan's Inter-Services Intelligence directorate, Lt. Gen. Ahmed Shuja Pasha.

In the talks, Mullen urged them to "investigate aggressively any and all possible ties to groups based in Pakistan," the statement said.

Analysts said the trip was designed to prevent a further deterioration in relations between the South Asian nations, something that might undermine the United States' broader war on terrorism.

Analysts said the American visits could ease tension between the two rivals. "I have a sense it will work," said Jawed Naqvi, a New Delhi-based correspondent with Pakistan's Dawn newspaper. "After all, neither side want confrontation."

Ramachandra Guha, author of "India After Gandhi," said a lot would depend on whether Rice is seen as relatively neutral or whether she appears to be joining India in bashing Pakistan. "If she's seen as someone who's just advising India, it won't work," he said.