Iran believes that a deal with Oman to reopen the Strait of Hormuz is “on the verge of being finalised”, potentially paving the way for a return to diplomacy with the United States.

Deputy foreign minister Kazem Gharibabadi said talks had finally “reached fundamental understandings” after both sides agreed on shipping routes following months of disruption in the vital waterway.

There was no immediate comment from Washington on the proposal, but president Donald Trump late on Wednesday portrayed ongoing talks positively and said a deal on Hormuz was imminent.

He told FOX5 that talks over the strait were “moving along nicely” and that the strait “is going to be open very soon”.

That came amid reports that Iran had issued a warning to its Gulf neighbours threatening fierce retaliation in the event of more US strikes, while insisting the regime remained open to diplomacy.

Iranian foreign minister Abbas Araghchi reportedly warned Gulf states that any new US attack on its territory would prompt strikes against critical energy infrastructure across the region, as Tehran seeks to raise the cost of military action by threatening Washington's closest regional allies.

“The Iranian warning was unequivocal: if America targeted Iran's infrastructure, they would retaliate by striking Gulf energy facilities and other regional targets,” one Gulf source told the Reuters news agency.

His message was consistent in every conversation, a diplomatic source said: "We're ready to retaliate, but finding a diplomatic solution is the best way to avoid wider escalation and destruction across the region."

Saudi Crown Prince Mohammed bin Salman subsequently spoke with Trump, urging him to delay military action, return to negotiations, secure a ceasefire and pursue a diplomatic settlement, the senior diplomat and Gulf sources said.

Insiders near the proposed deal to reopen the Strait of Hormuz were already skeptical of its merits as Iran and Oman closed in on an agreement.

Under the latest proposal, Tehran would be able to intervene if necessary with any inbound traffic, while outbound traffic would follow a route between Iran and Oman, with exit clearance granted through Oman after notifying Iran, a senior Iranian source told Reuters this week.

Regional sources said that key details were yet to be finalised, however, and that Iran still seeks to collect fees from ships navigating the strait - a recurring issue at odds with Washington’s position that it should be free.

Gulf negotiators have insisted that any payment of fees be voluntary, while a senior Iranian official said that the Islamic Republic is seeking fees of 5-7% of the price of cargoes from ships using the strait.

Any deal giving Iran authority over the strait would hand huge leverage to the regime and could yet stoke tensions with the US, where officials have said they will never agree to Tehran controlling such a vital trade route.

Four industry sources also said on Thursday that the proposed deal between Iran and Oman is not easily workable due to US sanctions and restrictive insurance clauses on any payments.

The world's leading shipping associations said in an open letter this week that introducing compulsory charges “would establish a precedent that could undermine the internationally recognised legal framework governing straits used for international navigation and transit passage”.