Relations between the two countries are at a turning point after the Indian Government alleged Pakistani involvement in the attack and summoned the head of Pakistan's highest intelligence agency to assist with investigations. The Pakistani Government initially agreed to this demand but then decided to send a lower ranking representative instead.

The senior security official was quoted in the Pakistan media as saying that if cross-border tensions continue to rise, "the war on terrorism won't be our priority. We'll take out everything from the western border. We won't leave anything here. [The] next two days will prove crucial to relations."

If the Pakistani army acts on this threat, about 100,000 troops might be diverted away from fighting Taliban militants along its north-western border. A redeployment of that scale would be a setback to western forces based in southern Afghanistan, including a large Australian troop contingent, who are battling Taliban insurgents with links to militants on the Pakistan side of the border.

The US Secretary of State, Condoleezza Rice, is understood to have spoken to the Indian foreign minister, Pranab Mukherjee, and urged India not to escalate tensions with Pakistan.

There were hopes the return of democracy in Pakistan this year would pave the way for improved ties between the traditional rivals, who have fought three wars since they both gained independence in 1947. However, Mr Mukherjee says the Mumbai attack has made efforts to improve relations "impossible."

After terrorists with links to Pakistan launched a brazen attack on the Indian parliament building in 2001, both countries mobilised a heavy contingent of troops along the border but a major conflict was avoided.

The Pakistan President, Asif Ali Zardari, attempted to soothe anger across the border during a rare interview with an Indian broadcaster, saying he had been "hurt" and was "bleeding" watching Mumbai's trauma.

"I stand with the people of India. I stand with the leadership of India. I am sorry that you are going through this," he said.

Mr Zardari also referred to the murder of his wife, Benazir Bhutto. "Your wound brings attention to my wound, it is also very recent," he said.

However, the Pakistan Foreign Minister, Shah Mehmood Qureshi, said the situation was "serious" and called on India not turn the attacks into a diplomatic conflict. "No evidence [of Pakistani involvement] has been provided so far … the Government of Pakistan and all the institutions of Pakistan are unanimous that Pakistan is not involved in the ghastly attack."

Mr Zardari had an emergency meeting with his Prime Minister, Yousaf Raza Gilani, and army chief, Ashfaq Parvez Kayani, late on Saturday to discuss the nation's response to the fallout from the terrorist attack.

Mr Gilani has since cancelled a trip to Hong Kong to concentrate on addressing the growing tensions. Wilson John, a security analyst with a Delhi think-tank, the Observer Research Foundation, said that even if there was no evidence of any involvement by the Pakistani state in the attacks, there was now great pressure to clamp down on terrorist groups operating within its borders.

"Over the past few years there have been efforts to bridge the gap of distrust between the two countries but that has now been broken," he said.

Many Indians are convinced Pakistan was behind the attacks. Soon after the last three terrorists occupying the Taj Mahal Hotel in Mumbai were shot dead by commandos on Saturday, a band of protesters gathered near the charred building chanting anti-Pakistan slogans.

There has also been an outpouring of anger on current affairs and TV chat shows against Indian politicians for an apparent indifference to ensuring the country was better prepared to combat terrorism.

The Home Minister, Shivraj Patel, who is responsible for combating terrorism, became the first political casualty of the terrorist attack when he resigned yesterday. He has been criticised for failing to prevent a string of terrorist attacks since May.

"Politicians fiddle while innocents die," read an editorial in the Times Of India . It challenged Indian politicians to do something "worthwhile" with their lives and come up with effective strategies to combat terrorism.

Even Bollywood has expressed its discontent. Producer Vinod Chopra claimed the Mumbai attack was due to "a total failure of the government" and starlet Aarti Chhabria said Mumbai's experience was "like being put in a torture chamber".

A senior state minister, R. R. Patil, stoked the present deep resentment towards politicians in India when he said in a media conference that the Mumbai attack was a "small incident" and that events of this nature were "common in big cities". There will be an early indication of voter response to the Mumbai attack as several states, including Delhi and part of Kashmir, went to the polls over the weekend.

The spate of terrorist attacks this year has been a political gift for the Hindu nationalist party, the BJP, which hopes to snatch government from the centrist, secular coalition, led by the National Congress Party, now in power. The coalition held meetings yesterday to discuss toughening anti-terrorist laws.

Rahul Bedi in Mumbaiwith Agence France-Presse