A hoax telephone call almost sparked another war between nuclear-armed India and Pakistan at the height of last month's terror attacks on Mumbai, officials and Western diplomats on both sides of the border said on Sunday.

Asif Ali Zardari, the Pakistani President, took a telephone call from a man pretending to be Pranab Mukherjee, India's Foreign Minister, on Friday, November 28, apparently without following the usual verification procedures, they said.

The hoax caller threatened to take military action against Pakistan in response to the then ongoing Mumbai attacks, which India has since blamed on the Pakistan-based militant group Lashkar-e-Taiba (LeT), they said.

Mr Zardari responded by placing Pakistan's air force on high alert and telephoning Condoleezza Rice, the US Secretary of State, to ask her to intervene.

But when Dr Rice called Mr Mukherjee, he said that he had not spoken to Mr Zardari and that his last conversation with Shah Mahmood Qureishi, the Pakistani Foreign Minister, had been quite civil.

"It's unbelievable, but true," said a Western diplomat familiar with the frantic diplomatic exchanges that eventually resolved the misunderstanding.

"It was a little alarming, to say the least."

The episode – reminiscent of Stanley Kubrick's 1964 film Dr Strangelove – dramatically illustrates how easy it would be for another war to break out between India and Pakistan, even accidentally, following the Mumbai attacks.

The two countries have already fought three since winning independence from Britain in 1947 and almost went to a fourth in 2002 after LeT militants attacked India's parliament, prompting both sides to mass troops on their common border.

Some officials and analysts fear the hoax may have been part of an elaborate plot to provoke a conflict between India and Pakistan, thereby diverting Pakistani forces away from the fight against Islamist militants near the Afghan border.

No-one on either side believes the call was a joke as people on both sides are acutely aware of the potential for war.

However, it remains unclear who placed the hoax call, from where, and why Mr Zardari's office appears to have disregarded standard operating procedures.

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