(Reuters) - Indian accusations of a Pakistani link to the attacks on Mumbai that killed nearly 200 people threaten to damage attempts to improve ties between the rivals.
Indian officials have said most, perhaps all, of the 10 attackers who held Mumbai hostage with frenzied attacks using assault rifles and grenades came from Pakistan, a Muslim nation carved out of Hindu-majority India in 1947.
An official in Islamabad said the next one to two days would be crucial for relations between the nuclear-armed neighbours. Pakistan has condemned the assaults and denied any involvement by state agencies.
After a final battle between militants and security forces inside the Taj Mahal, Mumbai's best-known hotel, a crowd of protesters outside pumped their fists and shouted "Our soldiers came and Pakistan ran away".
A senior Pakistani security official said Islamabad would divert troops to its border with India and away from fighting militants on the Afghan frontier if the tension spilled over.
"If something happens on that front, the war on terror won't be our priority," the official told reporters at a briefing.
"We'll take out everything from the western border. We won't leave anything there."
Elite Black Cat commandos killed the last of the gunmen on Saturday after three days of room-to-room battling inside the Taj Mahal, one of several landmarks struck in co-ordinated attacks on Wednesday night.
Hundreds of people, many of them Westerners, were trapped or taken hostage as the gunmen hurled grenades and fired indiscriminately. At least 22 of those killed were foreigners, including businessmen and tourists.
Nine gunmen and 20 police and soldiers were also killed.
A tenth militant caught alive told interrogators they wanted to be remembered for an Indian version of the Sept. 11, 2001, attacks on the United States, Times Now TV said, quoting an unidentified Defence Ministry official.
Indian Prime Minister Manmohan Singh has said "elements" in Pakistan may have been responsible for the attacks.
"The Congress calls upon Pakistan to honour its commitment and prevent the use of its territory for commission of acts of terrorism against India," his ruling Congress party coalition said after an all-party meeting late on Saturday.
India and Pakistan have fought three wars since independence and went to the brink of a fourth after a December 2001 attack on India's parliament that India also linked to Pakistan.
They embarked on a peace process in 2004 that has ground on for the past four years.
"These are sensitive moments," Pakistan Foreign Minister Shah Mehmood Qureshi told a news conference. "The situation is serious, let us not fool ourselves ... when the people in India feel this is 9/11 for India."
A high ranking security officer in Pakistan said tension with India was escalating rapidly. "They'll have clarity of thought and we'll have clarity of the situation in next 24-48 hours," he said.
India's internal politics are integral to the fallout from the attacks too. Singh is facing an election by May and renewed accusations from India's main opposition, the Hindu nationalist Bharatiya Janata Party, that Congress is weak on security.
"Brutal terror strikes at will. Weak government. Unwilling and incapable. Fight terror -- Vote BJP," said one election ad, written over a blood-red stain on a black background.
India said evidence was mounting to suggest the men who attacked Mumbai came by sea from Karachi, Pakistan's main port.
"Investigation carried out so far has revealed the hand of Pakistan-based groups in the Mumbai attack," Sriprakash Jaiswal, India's minister of state for home affairs, told Reuters.
Pakistani President Asif Ali Zardari, battling Islamic radicals in his own nation, told CNN-IBN television he would cooperate with the investigations.
"If any evidence comes of any individual or group in any part of my country, I shall take the swiftest of action in the light of evidence and in front of the world," he said.
India's Home Ministry said the official toll was 183 killed. Earlier, Mumbai disaster authorities said at least 195 people had been killed and 295 wounded.
The attacks struck at the heart of Mumbai, the engine of an economic boom that has made India a favourite emerging market.
The city of 18 million is also home to the "Bollywood" film industry, the epitome of glamour in a country blighted by poverty.