A man pretending to be India's foreign minister called Pakistan's president and talked in a "threatening" manner during the Mumbai terror attacks, prompting Pakistan to put its air force on high alert, a security official and a news report said Saturday. Dawn newspaper said authorities were investigating the circumstances of the hoax, which occurred as tensions spiked between the nuclear-armed neighbors during the attacks, which began Nov. 26 and have been blamed by India on Pakistani extremists. Indian officials were not immediately available to comment. The call by a man identifying himself as Indian Foreign Minister Pranab Mukherjee was put through to President Asif Ali Zardari on Nov. 28, said the security official, who declined to be identified citing the sensitivity of the issue. "India through diplomatic channels has informed the Pakistani Foreign Ministry that Pranab Mukherjee made no such call," he said. "Now what still needs to be checked is who made this threatening call."