US President Donald Trump says he has instructed negotiators “not to rush into a deal” with Iran, after earlier suggesting an agreement was close.

The deal under discussion reportedly involves a 60-day ceasefire extension, reopening the Strait of Hormuz and a plan for further negotiations over Iran’s nuclear programme.

In a social media post, Trump said “constructive” talks were proceeding but “both sides must take their time and get it right”.

Trump said on Saturday an agreement had been “largely negotiated”, prompting speculation an announcement could be imminent.

Iranian officials also signalled progress in talks over the weekend, with foreign ministry spokesperson Esmail Baghaei saying the two sides are both “very close and very far” from reaching an agreement.

According to US media, the mooted deal is not a final settlement, and instead leaves some of the thorniest issues to be negotiated later, including Iran’s demand for sanctions relief, its calls for the release of frozen Iranian funds, and Washington’s demands for Iran to curb its nuclear ambitions.

The reported deal has split Republicans, with some publicly arguing it is too lenient on Iran.

Senator Ted Cruz said it would be “a disastrous mistake”, while Roger Wicker, who chairs the Senate Armed Services Committee, said a 60-day ceasefire would mean “everything accomplished by Operation Epic Fury would be for naught!”

But Representative Mike Lawler, who sits on the House Foreign Affairs Committee, said the administration has managed to “force the remnants of this regime into a negotiation, a real negotiation”.

The US and Israel launched wide-ranging strikes on Iran on 28 February, sparking conflict across the Middle East. Iran responded by attacking Israel and US-allied states in the Gulf, and effectively closing the Strait of Hormuz, through which around 20% of the world’s oil and liquefied natural gas travels. The move sent oil prices soaring globally.

After a ceasefire was agreed in early April, the US established a blockade of Iranian ports which Trump says will remain “in full force and effect until an agreement is reached, certified, and signed”.

In Sunday’s post on Truth Social, Trump reiterated that Iran “must understand” it cannot develop a nuclear weapon. Tehran has repeatedly said its nuclear programme is solely for peaceful purposes.

Some reports in US media suggest the deal could see Iran agree to eventually hand over its highly-enriched uranium.

It is thought to have about 440kg (970 lbs) of uranium that is enriched up to 60% purity – a short process away from being enriched further to the weapons-grade 90%, which could allow Iran to create a nuclear bomb.

Iranian President Masoud Pezeshkian told state TV Iran was ready “to assure the world that we are not after a nuclear weapon.”

US Secretary of State Marco Rubio earlier said that “significant” but “not final” progress had been made in the negotiations. He hinted that progress over the past 48 hours 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 over a “final agreement”

Trump also described the deal as 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”.