Pakistani security officials told AFP on Sunday that the man killed on Saturday in the southwestern province of Balochistan, believed at the time to be Mansour, had just returned from Iran when his vehicle was attacked.
US President Barack Obama on Monday confirmed that Mansour had been killed in a US air strike, hailing his death as an "important milestone" in efforts to bring peace to Afghanistan.
Senior Taliban sources have also confirmed the killing to AFP, adding that a shura (council) was under way to select a new leader.
"The competent authorities of the Islamic republic deny that this person on this date crossed Iran's border and into Pakistan," he said.
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"Iran welcomes any positive action leading to peace and stability in Afghanistan," he added, without elaborating.
Pakistani identity documents found on the body of the man now known to be Mansour named him as Muhammad Wali, and showed he had left for Iran on March 28 and returned the day he was killed.
President Ashraf Ghani meanwhile arrived in Tehran today for the signing of a tripartite agreement between Iran, India and Afghanistan to turn Iran's southeastern port of Chabahar into a transit hub between the three countries, bypassing Pakistan.
Islamabad, which says it hosts many of the Afghan Taliban's top leadership to exert influence over them and bring them back to peace talks with Kabul, called the US drone attack a violation of its sovereignty.