Condoleezza Rice, the US Secretary of State, urged India and Pakistan to cooperate in investigating last week's Mumbai attacks as she arrived in Delhi to try to avert another conflict between the nuclear-armed neighbours.

Amid intensifying diplomatic efforts, US Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, also flew into Islamabad to press Pakistani leaders not to let tensions with India detract from their campaign against Islamist militants on the Afghan border.

However, tensions between Delhi and Islamabad looked set to escalate after Asif Ali Zardari, the Pakistani President, said he doubted India's assertion that the one militant captured in Mumbai was from Pakistan.

"We have not been given any tangible proof to say that he is definitely a Pakistani," he told CNN's Larry King Live, adding that, if given evidence, his government would take action.

"The gunmen, whoever they are, they are all stateless actors who are holding hostage the whole world," he said. "The state of Pakistan is, of course, not involved. We are part of the victims."

Mr Zardari also turned down India's request to extradite 20 alleged terror suspects, offering instead to try them in Pakistan if there was any evidence of wrongdoing.

His remarks are sure to anger India and alarm the US and its allies, which fear that a military confrontation between Delhi and Islamabad would scupper the campaign against Islamist militants in Afghanistan and northern Pakistan.

India said yesterday that it was not considering military action against Pakistan in response to last week's attacks, which it blames on the Pakistan-based militant group Lashkar-e-Taiba (LeT).

But it reserved the right to protect its territorial integrity, and gave warning that it could suspend a five-year-old peace process between the neighbours, which have fought three wars since independence in 1947.

Dr Rice's aim is to prevent a repeat of the crisis that unfolded after LeT militants attacked India's Parliament in 2001, prompting India and Pakistan to mass troops on their common border in what came dangerously close to a fourth war.

"This is the time for everybody to cooperate and do so transparently, and this is especially a time for Pakistan to do so," she told a news conference shortly after arriving in the Indian capital.

She is due to meet Manmohan Singh, the Indian Prime Minister, as well as India's foreign and home ministers and LK Advani, the leader of the Hindu nationalist Bharatiya Janata Party (BJP), the main opposition party.

She is expected to urge restraint from all sides, but especially the BJP, which is keen to exploit public anger over the Mumbai attacks ahead of a national election, due by May.

The BJP, which was in power when India and Pakistan almost went to war in 2002, has urged India to respond the Mumbai attacks in the same sort of way that the United States did to 9/11.

Pranab Mukherjee, the Foreign Minister, said yesterday that military action against Pakistan was not being discusssed.

However, India has demanded that Pakistan take "strong action" against the militants and extradite 20 fugitives, including Dawood Ibrahim, a Mumbai mafia don with links to Lashkar-e-Taiba.

It has told Pakistan that the attack was planned by Muzzamil Yousaf and Asrar Shah, two Lashkar-e-Taiba activists based in Pakistan, and approved by Abdur Rehman Makki and Hafiz Muhammad Saeed, their leaders.

Pakistan has said in the past that it will not hand its citizens to India and denied that Mr Ibrahim, an Indian national, was on its soil.

Mr Saeed, in his first public comments on the Mumbai attacks, denied any involvement yesterday. "India has always accused me without any evidence," he said in an television interview.

Pakistan has also cautioned that if India masses troops on its border, it would respond by diverting troops fighting al-Qaeda and Taleban militants in its northwestern tribal areas near the Afghan border, potentially jeopardising Nato and U.S. operations in Afghanistan.

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