A mysterious night-time telephone call brought India and Pakistan, two nuclear armed countries, to the brink of war at the height of the crisis over the Mumbai terror attacks, it was revealed yesterday.

According to the Pakistani authorities, a "threatening" call was made by the Indian government, ostensibly from the foreign minister, Pranab Mukherjee, to Pakistan's president, Asif Zardari, on Friday November 28, two days after the drama in Mumbai began. India had by then declared that all the militants who had stormed its commercial capital were from Pakistan.

The heated conversation left Zardari believing that India was about to attack his country, reportedly pushing Pakistan's armed forces to high alert. Given Pakistan's inferiority in conventional forces, analysts believe it could respond with nuclear weapons to an Indian attack.

Zardari quickly mobilised western leaders in an attempt to avert war, telephoning the US secretary of state, Condoleezza Rice, and Britain's foreign secretary, David Miliband, among others, who in turn frantically called New Delhi. Rice reportedly telephoned Mukherjee in the middle of the night and demanded: "Why have you threatened war?"

Yesterday Mukherjee lashed out at Pakistan, denying that he had made any such call. "I can only ascribe this series of events [the story of the call] to those who wish to divert attention from the fact that a terrorist group, operating from Pakistani territory, planned and launched a ghastly attack on Mumbai," he said.

Pakistan's government insists that the phone call came from a number in India's ministry of external affairs. Wajid Hasan, Pakistan's ambassador in London, said a caller ID system in the presidency was used to identify the origins of the call. "They did it [made the call]. It was not a hoax call, but an instrument of psychological warfare. They were trying to scare Pakistan, test the waters for our reaction."

News of the phone call hysteria was leaked to a group of Pakistani journalists at a briefing by the Indian embassy in Islamabad, in an apparent attempt to make Zardari's government look shambolic. Pakistan's information minister, Sherry Rehman, said at the weekend: "The government of Pakistan condemns such efforts aimed at using the media for negative diplomacy at a time when tensions are running high."

It is unclear who made the call if it did not come from the Indian ministry. Indian officials suggest it came from Pakistan's Inter-Services Intelligence agency, trying to sever relations between the governments of the two countries.

John McCain, the US senator, arrived in Pakistan at the weekend from New Delhi, where he met the Indian prime minister, Manmohan Singh, and told Pakistani journalists that India was ready to order air strikes. At a lunch with senior reporters in Lahore, McCain said Indian officials had told him they had evidence of the involvement of former ISI officers in the planning and execution of the Mumbai assault.

Speaking on Fox news, Rice said: "There is evidence of involvement somehow on Pakistani soil ... The United States expects the full and complete cooperation of Pakistan, and Pakistani action."

Yesterday Pakistani security forces raided a camp used by Lashkar-e-Taiba, the Kashmiri extremist organisation blamed by India for the attack on Mumbai. Local sources told Reuters that helicopter-borne forces had taken over the camp in the outskirts of Muzaffarabad, the capital of Pakistani Kashmir.