US Secretary of State Condoleezza Rice arrived in New Delhi on Wednesday to try to ease India-Pakistan tensions over the Mumbai attacks, as US intelligence blamed a Pakistan-based militant group.
Pakistan's president, meanwhile, said any of the 20 suspects wanted by India would be tried in Pakistan if there was evidence of wrongdoing.
Rice, America's top diplomat, said Pakistan must act with urgency and resolve in co-operating with Indian investigations into the Mumbai attacks.
"We have to act with urgency and act with resolve. Pakistan needs to act with urgency and with resolve," she told reporters prior to talks with Indian Foreign Minister Pranab Mukherjee and Prime Minister Manmohan Singh on Wednesday.
US officials have pointed the finger at Pakistani-based groups in the attacks and have pressured Islamabad to co-operate in the investigation.
As evidence of the militants' links to Pakistan mounted, authorities said on Tuesday that ex-Pakistani army officers trained the gunmen behind the attacks - some for up to 18 months - and the group set out by boat from the Pakistani port of Karachi.
"It appears that it was a suicide attack," Mumbai police commissioner Hasan Ghafoor said, providing no other details about when the gunmen left Karachi, or when they hijacked the trawler that carried them into Mumbai.
The revelations came as a senior Bush administration official said India had received a warning from the United States that militants were plotting a waterborne assault on Mumbai.
The Indian government, already facing accusations of security and intelligence failures, has demanded that Pakistan take action against those responsible and asked that 20 suspected terrorists believed living in the country be handed over.
President Asif Zardari said he would "look into all the possibility of any proof" about the suspects sought by India and insisted they would be dealt with under Pakistani law.
"At the moment, these are just names of individuals - no proof and no investigation," he said on Tuesday in an interview with CNN's Larry King.
"If we had the proof, we would try them in our courts and we would try them in our land and we would sentence them."
India has stepped up the pressure on its neighbour after interrogating the only surviving attacker, who told police that he and the other nine gunmen had trained for months in camps in Pakistan operated by the banned Pakistani militant group Lashkar-e-Taiba.
American officials have said there is reason to suspect that the terror attacks were the work of a group at least partly based in Pakistan, although they've stopped short of mentioning Lashkar by name.
US National Intelligence Director Mike McConnell said on Tuesday the same group that carried out last week's attack was believed to be behind the Mumbai train bombings that killed more than 200 two years ago.
While he didn't identify the group, the Indian government has attributed the 2006 attack to Lashkar and the Students Islamic Movement of India.
Last week's attacks against hotels, a restaurant and other sites across Mumbai killed 188 people and injured more than 300.
The rampage has exposed weakness in India's security and intelligence agencies, which apparently failed to act on multiple warnings ahead of the Mumbai attacks - "a systemic failure," said Indian navy chief Sureesh Mehta.
India's foreign intelligence agency also had warnings as recently as September that Pakistan-based terrorists were plotting attacks on Mumbai, according to a government intelligence official familiar with the matter.
The information, intercepted from telephone conversations apparently coming out of Pakistan, indicated that hotels might be targeted but did not specify which ones, the official said.
CNN and other US networks this week reported that the United States had warned India in October that hotels and business centres in Mumbai would be targeted by attackers coming from the sea.
One US intelligence official even named the Taj Mahal hotel, one of 10 sites hit in the 60-hour siege by gunmen, as a specific target, ABC television said.
It said Indian intelligence officials intercepted a phone call on November 18 to an address in Pakistan used by the head of Lashkar-e-Taiba, revealing a possible attack from the sea.
At the Taj Mahal hotel, where the siege finally ended Saturday morning, authorities tightened security in the weeks before the attacks after being warned of a possible threat.
At the Oberoi hotel, the second five-start hotel the gunmen seized, the shopping arcade opened on Wednesday for the first time since the attacks.
Indian officials say evidence from the interrogation of the surviving attacker, Ajmal Qasab, points to Lashkar, which was outlawed in 2002 in Pakistan under US pressure.
Qasab told police his group trained for about six months in Lashkar camps in Pakistan, learning close-combat techniques, hostage-taking, handling of explosives, satellite navigation.
The training was "meticulous and rigorous," said a security official who spoke on the customary condition of anonymity.
The official said the gunmen sailed from Karachi in a Lashkar vessel that brought them to the waters near an Indian vessel they hijacked, the MV Kuber.
Police were questioning the owner of the MV Kuber, from which investigators recovered a global positioning system that belonged to the attackers.
