A day after US President Donald Trump touted that an agreement was near and the details could be announced “shortly”, the White House has now walked back some of its earlier optimism.US President Donald Trump too earlier today said he had directed American negotiators “not to rush into a deal”. (AFP)A senior US official, according to Axios, said that the White House now believes that a deal with Iran might take several days to get approval by Tehran's leadership, including Supreme Leader Mojtaba Khamenei. This comes even as Iranian President Masoud Pezeshkian earlier today asserted that no decision was made in the Islamic Republic without the permission of the Supreme Leader.Meanwhile, a senior administration official said the details of the agreement was still under negotiation, and therefore no deal was expected to be signed on Sunday, CNN reported.‘Back and forth on specific details’Regarding the delay in reaching an agreement, the senior Trump administration official said there was still “back and forth on specific details” between Washington and Tehran, according to an Axios report.The official said that there were still details which needed to be worked out. “Some words we care about, Some words they care about,” the official stated, adding that the “slow and opaque” nature of Iran's decision-making system could stretch the talks by another few days.“Our understanding is that the Supreme Leader, Mojtaba Khamenei, has endorsed the broad template of the deal. Whether this becomes an agreement is still an open question,” Axios cited the official as saying.Uncertainty over final deal remainsWhile both sides have noted that progress has been made and a deal is near, they have also remained cautious of blind optimism. Iran's Tasnim news agency warned Sunday that the deal may be derailed, citing alleged US “obstruction” to key clauses. Meanwhile, US officials also acknowledge that the deal has not been finalised and could fall apart.“We are in a very good place — but there are ways in which the deal can be undermined,” a senior US official told Axios. US President Donald Trump too earlier today said he had directed American negotiators “not to rush into a deal”, and said “both sides must take their time and get it right.”Among the key issues is Iran's nuclear program, with the US administration official saying Tehran has reportedly agreed in principle to reopen the Strait of Hormuz and dispose of its stockpile of highly enriched uranium. Iran is yet to confirm this, with the Tehran leadership having maintained that the nuclear issue was not a part of the talks at this stage.