Pakistan's army chief Asim Munir spoke with US President Donald Trump last week, according to three Pakistani sources, days before Munir was expected to hold talks in the Iranian capital Tehran on Monday.
The call, which has not been previously reported, came as the US threatened to roll out major economic sanctions targeting Iran and its trade partners.
The White House Office of the Press Secretary did not immediately respond to a request for comment. It was unclear what Munir and Trump discussed.
Pakistan's military confirmed the visit on Monday, saying it was "part of Pakistan’s efforts to promote regional peace and stability." Iranian officials had confirmed the visit on Sunday, saying it was focused on security and peace.
Trump last week warned of economic consequences against any country that provided "any type of lifeline to Iran" as he seeks to isolate the country. Iran in turn vowed to shut down all oil exports from the Gulf.
Pakistan, which has played a key mediating role between the US and Iran this year, has remained a trading partner of Iran throughout the recent fighting.
Munir was expected to meet with people close to Iran's Supreme Leader Mojtaba Khamenei on Monday, one Pakistani source said.
Pakistan's earlier mediation efforts between the US and Iran resulted in an interim peace agreement signed in June. But the Islamabad Memorandum quickly faltered, amid new fighting between Iran and the US that has threatened to spiral into a wider regional conflict in recent weeks.
"There is a trust deficit on both sides," a third Pakistani source said about the US and Iran, adding that Munir's aim was to mitigate the lack of mutual trust on Monday.
