Mediators were trying to salvage diplomacy aimed at ending the Middle East war after US President Donald Trump declared the ceasefire over, with a Qatari delegation in Iran and Tehran's top diplomat travelling to Oman.
An exchange of fire this week rocked an already fragile agreement that was supposed to help pave the way for a permanent end to the conflict, which broke out in late February with massive US-Israeli strikes on Iran.
While there have been no direct talks between Tehran and Washington since last month, Iranian media reported that a delegation from mediator Qatar travelled to Iran on Friday.
The visit follows Trump saying talks would continue, despite previously labelling them "a waste of time".
"Iran has asked us to continue 'talks'. We have agreed to do so, but the United States has stated to them, in no uncertain terms, that the Cease Fire is OVER!" Trump posted on his Truth Social platform.
In a later post he ramped up the rhetoric, threatening to "completely decimate" Iran if it attempted to assassinate him.
Iran's foreign minister Abbas Araghchi arrived in Oman, which mediated US-Iran negotiations before the war broke out, on Saturday for talks on the critical Strait of Hormuz.
The strait has been a key sticking point in negotiations with Washington, and Araghchi insisted Iran had stuck to its end of the bargain.
Tehran "has so far kept its word, unlike the so-called US Treasury Secretary who is violating Para 9 of the MoU", Araghchi said.
That refers to part of the US-Iran memorandum of understanding which states that Washington "will not impose any new sanctions, and will not deploy additional forces in the region", pending a final deal between the foes.
This week, the US Treasury Department revoked a temporary sanctions waiver for Iranian oil, cancelling a license announced in June that had allowed Tehran to produce, sell and deliver crude oil and related products until August 21.
"That violation follows other violations and missteps by the United States. Reality check: There can only be mutual compliance," Araghchi said.
- Hormuz deadline -
US and Iranian delegations have held one round of direct talks in Switzerland since the signature of their memorandum of understanding, as well as indirect negotiations in Qatar, but there has been no sign of diplomatic progress since.
A key roadblock to a final deal is the future of the Hormuz strait, which Iran closed to commercial ships during the war in retaliation for US-Israeli strikes.
The waterway is a key conduit for oil and gas exports out of the Gulf, and its closure has heavily impacted the world economy.
Iran insists on controlling the passage of ships and has announced plans to charge fees, saying there will be no return to the free navigation of the pre-war era.
Washington says Hormuz is an international waterway and any fees would be unacceptable.
News outlets Axios and Politico reported that Washington has given Tehran until Saturday to stop firing on commercial ships transiting Hormuz and acknowledge the waterway is open.
This week's exchange of strikes was sparked after Iran was accused of targeting three vessels that it said had deviated from its approved route.
The attacks prompted Washington to launch a heavy round of bombing in Iran, hitting around 90 targets across the country, according to the US military.
The American strikes killed 17 people, Tehran's health ministry said Saturday, and injured 115 more. They also triggered a wave of reprisals by Iran against Gulf countries that host American military bases.
- 'Hard-earned peace' -
Despite being one of the Gulf nations targeted during the war, Qatar has spearheaded efforts to get diplomacy back on track.
Iran's Tasnim news agency reported Friday that a Qatari delegation was visiting Tehran to "try to reinforce Qatar's role as a mediator following events on Tuesday".
Prime Minister Shehbaz Sharif of Pakistan, which has also been mediating, held a call with Qatar's emir on Friday to discuss the recent escalation, his office said.
The Pakistani leader said he had also spoken with Iran's President Masoud Pezeshkian, urging him to safeguard the "hard-earned peace" in the region.
But Iran's chief negotiator in talks with Washington, Mohammad Bagher Ghalibaf, struck a defiant tone.
"Ending the war is a priority for the countries of the world, but everyone must know that this confrontation will never end with Iran's surrender," Iran's ISNA news agency quoted him as saying.
Iranians, he said, were "fully prepared to defend ourselves".
