US Vice President JD Vance will not travel to Switzerland as scheduled for talks on Friday following up on the deal to end the war with Iran, according to the White House.
The signing of the accord this week was intended to end the conflict in Iran, reopen the Strait of Hormuz and begin a 60-day period for talks on wider issues, including Tehran's nuclear program, said AFP.
At the same time, the deal was to end the fighting in Lebanon, but new clashes have flared between Israeli forces and Iran-backed Hezbollah militants.
It has also appeared increasingly unlikely that a signing ceremony between the United States and Iran, originally slated for Switzerland on Friday, will take place as planned.
"The logistics of these negotiations have never been simple or predictable. As of now the Vice President is not departing tonight," a White House spokesperson said of Vance late Thursday.
"We look forward to beginning technical talks as soon as possible."
In Iran, the Tasnim agency said "nothing has been confirmed" about the Iranian delegation's trip to Switzerland.
The agreement has been signed separately by US President Donald Trump and his Iranian counterpart Masoud Pezeshkian.
Iran's supreme leader Mojtaba Khamenei said Thursday that he had approved the agreement, despite reservations, even as the United States lifted a blockade of Iranian ports.
Mojtaba Khamenei, who took over after his father and longstanding ruler Ali Khamenei was killed in an airstrike on the first day of the war on February 28, said in a written statement that he held a "different view" on the deal, without elaborating.
"But I issued my permission due to the commitment" made by officials including Pezeshkian to "protect the rights of the Iranian nation".
"Face-to-face negotiations" with the United States will be held in the future, but that does not "mean accepting the enemy's point of view", he added.
On Friday, Iran's chief negotiator Mohammad Bagher Ghalibaf warned that Tehran would give a "decisive" response if the agreement was breached.
- 'Maybe they start fighting again' -
American forces on Thursday lifted their naval blockade of Iranian ports that had prevented ships from sailing to or from the Iranian republic, the US military said, noting that American warships "will remain in the general area".
Activity was still muted in the Strait of Hormuz, the strategic bottleneck for energy shipments that Iran blockaded during the conflict.
Three Saudi oil tankers left the Gulf through the strait on Thursday, maritime trackers said, as did a French vessel loaded with liquefied natural gas.
Iranian state TV, citing a statement from the country's Supreme National Security Council, said that ships "seeking passage through the Strait of Hormuz must submit their request" to a new government body tasked with overseeing the waterway.
In keeping with the terms of the deal, it added, "no fees whatsoever will be collected from applicants for a period of sixty days".
The deal should bring an end to the current US-Israeli conflict with Iran, which saw five weeks of all-out war until a ceasefire was struck in early April.
But fighting has continued in Lebanon, with Tehran-backed Hezbollah saying on Friday that its fighters destroyed three Israeli tanks in the country's south and that clashes were "ongoing".
Israel has yet to confirm if its tanks were hit.
Three people were also killed in Lebanon by Israeli drone strikes, the country's official National News Agency reported on Thursday.
Hezbollah drew Lebanon into the Middle East war in March by attacking Israel to avenge the killing of Iran's supreme leader at the start of the US-Israeli campaign.
Some in Tehran were downbeat at the prospects for peace.
"I have no hope that this is a lasting agreement. Maybe after the 60 days they start fighting again," said Mina, 54, a psychologist from Tehran.
Her sentiment was shared by French President Emmanuel Macron, who presided over the signing at the Palace of Versailles in what he described as a "spontaneous" move by Trump.
Macron said he did not believe that the war was "totally finished".
- 'What does that get us?' -
Under the text, Washington commits to immediately waive oil sanctions crippling Iran's economy.
And once a final agreement is reached on Iran's nuclear program, the United States will facilitate the release of a $300 billion reconstruction fund supported by regional nations, the deal says.
Trump's decision to end the war, in which 13 US service members were killed and a vast proportion of US ammunition stockpiles was used, has unsettled some of his allies at home.
US Senator Bill Cassidy from Trump's Republican Party described it as the "worst foreign policy blunder in decades".
But Trump argued that using military force to wring more concessions out of Tehran would have been counterproductive.
"The only way I can get tougher is if I go in there for another two or three weeks and continue to bomb the hell out of 'em. Right? But what does that get us? The Strait of Hormuz will not be open," he told Axios.
"We wouldn't have oil for months," he said. "This is the kind of thing that could cause a worldwide depression."
