Pakistan put its forces on high alert after someone pretending to be India's foreign minister made a phone call to President Asif Ali Zardari threatening war after the Mumbai attacks began, Dawn newspaper said on Saturday. “It's true,” a diplomat with knowledge of the exchanges told Reuters when asked whether the report was correct. Dawn said the Dec. 28 caller threatened military action unless Pakistan acted immediately against the perpetrators of the slaughter in Mumbai, launched two days earlier. For the next 24 hours nuclear-armed Pakistan's air force was put on “highest alert” as the military watched anxiously for any sign of Indian aggression, the report said. Dawn said the caller, posing as Indian Foreign Minister Pranab Mukherjee, also tried to telephone US Secretary of State Condoleezza Rice, but due to specific checks by US officials the call was not put through. According to Dawn, Rice called Mukherjee in the middle of the night to ask why he had adopted such a a threatening tone, but he assured her that he had not spoken to Zardari. Mukherjee said his discussions with Pakistani Foreign Minister Shah Mehmood Qureshi, who was in New Delhi that day, had been cordial. There were frantic phone calls between Washington, Islamabad and New Delhi to cool the temperature and by the evening of Nov. 29, calm had been restored. Dawn said Zardari's staff had bypassed usual verification checks for a call for the president, but the government said Zardari received the call after it was properly verified that it originated from India's Ministry of External Affairs. “It is not possible for any call to come through to the president without multiple caller identity verifications,” Information Minister Sherry Rehman said in a statement. “In fact the identity of this particular call, as evident from the CLI (caller's line identification) device, showed that the call was placed from a verified official Phone Number of the Indian Ministry of External Affairs”. The newspaper said Indian officials had denied to US counterparts that the call came from its ministry and said the number could have been manipulated. It was during the hours of uncertainty that Pakistan rescinded its offer to send its Inter-Services Intelligence agency chief to India to help investigate the Mumbai attacks. Senior Pakistani security officers referred to the aggressive tone taken by the Indian foreign minister in a briefing to journalists on Nov. 29. They warned, in a clear message to the US, that if Pakistan felt threatened it would move troops from the Afghan border, where they are fighting Taleban and Al-Qaeda, to the Indian border and abandon the war on terrorism.