US Secretary of State Marco Rubio has voiced hope of progress on ending the US-Israeli war on Iran, with mediator Pakistan's army chief due to arrive in Tehran for talks.
The expected visit by Field Marshal Asim Munir, a powerful figure with a growing role in Pakistan's foreign relations, comes a day after US President Donald Trump warned that negotiations to end the war were on the "borderline" between a deal and renewed strikes.
"I believe the Pakistanis will be travelling to Tehran today. So hopefully that'll advance this further," Rubio told reporters on Thursday.
"There's some good signs," he said. "I don't want to be overly optimistic ... So, let's see what happens over the next few days."
An Islamabad-mediated ceasefire on April 8 halted the war launched weeks earlier by the US and Israel, but negotiation efforts have so far failed to yield a lasting peace agreement.
A war of words has taken the place of open conflict but the impasse continues to weigh on the world economy, leaving everyone from investors to farmers in a painful state of uncertainty.
On Thursday, Iran's ISNA news agency said Munir's visit was aimed at continuing "talks and consultations" with Iranian authorities, without providing details. Other Iranian media carried the same report.
Pakistan hosted in April the only direct negotiations between US and Iranian officials to take place since February 28, the day the war began.
Munir was at the centre of the action during that round of talks, greeting both delegations on their arrival and displaying remarkable bonhomie with US Vice President JD Vance.
But the talks ultimately failed, with Iran accusing the US of making "excessive demands".
Since then, the two sides have exchanged multiple proposals, with the threat of renewed war looming all along.
"It's right on the borderline, believe me," Trump told reporters on Wednesday. "If we don't get the right answers, it goes very quickly. We're all ready to go."
He said a deal could come "very quickly" or "in a few days", but warned Tehran would have to provide "100 percent good answers".
Rubio also criticised NATO allies for their refusal to help US' war against Iran.
'Forceful response'
Tehran's chief negotiator Mohammad Bagher Ghalibaf on Wednesday accused Washington of seeking to restart the war, warning of a "forceful response" if Iran were to be attacked.
Iran's foreign ministry spokesman Esmaeil Baqaei said Tehran was examining points received from Washington, while repeating Tehran's demands for the release of its assets frozen abroad and an end to a US naval blockade.
Trump is under political pressure at home as energy costs rise.
The Pakistan-brokered ceasefire halted the fighting but has not reopened the Strait of Hormuz, the vital waterway that normally carries about a fifth of the world's oil and liquefied natural gas.
The future of Hormuz remains a key sticking point in the negotiations, with fears growing that the global economy will feel more pain as pre-war oil stockpiles run down.
Iran imposed the blockade of Hormuz as part of its retaliation in the war, allowing only a trickle of vessels through in recent weeks while introducing a toll system.
Iran's new body overseeing Hormuz said its claimed area of control extends to Emirati waters, drawing a sharp rebuke from Abu Dhabi.
Relations between Iran and the United Arab Emirates have been severely strained since the war, after Tehran launched missile and drone strikes against Gulf countries in response to US-Israeli war.
Hormuz carries around a third of global fertiliser shipments, raising concerns of higher food prices and shortages if the closure drags on.
