TENRAN - Iranian foreign ministry spokesman Esmaeil Baqaei cautioned that the visit did not mean "we have reached a turning point or a decisive situation" with "deep and extensive" disagreements remaining, according to Iran's ISNA news agency.
US Secretary of State Marco Rubio had earlier voiced hope of progress toward ending the war, which began on February 28 with US-Israeli strikes on Iran and has led to competing blockades around the strategic Strait of Hormuz, roiling the global economy and pushing up energy prices.
Weeks of negotiations since an April 8 ceasefire -- including historic face-to-face talks hosted by Islamabad -- have still not produced a permanent agreement or restored full access to the strait - through which a fifth of global oil shipments normally pass.
President Donald Trump has described the stop-start negotiations this week as teetering on the "borderline" between a deal and renewed attacks.
The president on Friday said he would miss his son's wedding this weekend due to "circumstances pertaining to government", as US outlets Axios and CBS News reported the White House was considering strikes, although both added a final decision had not been made yet.
Pakistan's military said Field Marshal Asim Munir had "arrived in Tehran as part of ongoing mediation efforts".
The army chief was welcomed by Iran's Interior Minister Eskandar Momeni and his Pakistani counterpart Mohsin Naqvi, who had been in Tehran on two separate visits in the past week, meeting with the Iranian president and foreign minister.
"In recent days, many countries -- both regional and non-regional -- have been trying to help bring the war to an end... However, Pakistan remains the official mediator," said the Iranian foreign ministry's Baqaei.
Iran's foreign minister Abbas Araghchi said Tehran was engaged in the diplomatic process despite what he called "repeated betrayals of diplomacy" by the US and "military aggression against Iran", according to Iranian news agency Tasnim.
"Despite its strong suspicion of the United States, the Islamic Republic of Iran has entered this diplomatic process with a responsible approach and with all seriousness and is striving to reach a reasonable and fair result," Araghchi said.
Hormuz squeeze
Rubio, speaking on the margins of a NATO meeting in Sweden, said there had been "some progress" in the talks, but warned that Washington was "not there yet".
"It may not" change, Rubio said. "We're dealing with a very difficult group of people. And if it doesn't change, then the president's been clear he has other options."
Rubio said Trump "prefers the negotiated option" but had expressed concern that a deal "maybe...is not possible".
Israel and Hezbollah have continued to fight despite a ceasefire, with Israel striking Lebanon on Friday. (Credit: AFP)