Jaroslav Lukiv
Reuters
US President Donald Trump has instructed his negotiators "not to rush into a deal" with Iran, after reports suggested an agreement between the two sides was close.
In a social media post, Trump said "constructive" talks were proceeding but added that "both sides must take their time and get it right".
The US leader added Tehran "must understand" it cannot develop a nuclear weapon, a message supported by his Israeli counterpart Benjamin Netanyahu in a post on Sunday.
It came after comments from US and Iranian officials over the weekend signalled an apparent convergence between Washington and Tehran on elements of a peace deal.
Earlier, US Secretary of State Marco Rubio said "significant progress" had been made, but there was still "work to do".
Meanwhile, Iranian foreign ministry spokesperson Esmail Baghaei said on Saturday progress did not mean agreements would be reached on key issues and accused the US of "contradictory statements".
Israeli and the US began massive air strikes on Iran on 28 February, while Tehran retaliated by firing drones and missiles at Israel and US targets in countries across the Gulf.
A ceasefire agreed in April meant to facilitate talks has largely been observed despite occasional exchanges of fire.
Some US media outlets reported that no agreement between the two countries was expected to be signed on Sunday, citing officials.
Neither Washington nor Tehran have officially confirmed details of a potential deal, but reports have started to emerge on some possible elements.
A 60-day ceasefire extension and the reopening of the Strait of Hormuz are among those believed to be included, according to US outlet Axios.
Iranian media reports say there are still "one or two" points of disagreement in the potential deal.
In Sunday's post on Truth Social, Trump said the negotiations with Iran "are proceeding in an orderly and constructive manner, and I have informed my representatives not to rush into a deal in that time is on our side".
"Both sides must take their time and get it right. There can be no mistakes!"
Trump also said Iran "must understand" it cannot develop a nuclear weapon, a stance he has frequently reiterated and that is shared by Israel and other Western allies.
The US and its Western allies suspect that Iran is seeking to develop a nuclear weapon by enriching uranium - but Tehran has said its nuclear programme is solely for peaceful purposes.
In his social media post, the US president also said Washington's blockade of Iranian ports "will remain in full force and effect until an agreement is reached, certified, and signed".
The US military has been enforcing its blockade to exert pressure on Tehran to agree to Washington's terms.
For its part, Iran has continued to control the Strait of Hormuz, effectively closing the vital waterway through which around 20% of the world's oil and liquefied natural gas travels.
The move, which Iran has said is in retaliation for the Israeli-US attacks, has sent oil prices soaring globally.
Speaking earlier, Rubio said that "significant" but "not final" progress had been made in the negotiations.
He hinted at good news on Hormuz, saying that progress over the past 48 hours - if it works - could result in a "completely open strait... without tolls".
On Saturday, Baghaei told state television that Iran was in the process of finalising a "memorandum of understanding" which would allow additional talks so that "ultimately a final agreement can be reached".
Trump also mentioned a "memorandum of understanding" in a Truth Social post on Saturday.
Pakistan's Deputy Prime Minister Ishaq Dar, who has been mediating talks, has said that recent negotiations are "grounds for optimism" that a positive outcome is "within reach".
