Iran has rejected UN-backed plans for the mass evacuation of ships through the strait of Hormuz , creating a new threat to the free passage of commercial ships through the strait.

The proposal, backed by Oman, was potentially the first phase of a broader Omani proposal to consult on setting up a new management of the strait based on voluntary fees and modelled on the Malacca and Singapore strait mechanism.

The intervention showed that Oman and Iran’s visions for the strait may differ, although they were consulting each other to try to align their plans.

Iran’s intervention also damaged efforts led by Saudi Arabia to convene a conference to normalise relations between the Gulf States and Iran in a new proposed non-aggression pact.

Shipping through the strait had been steadily increasing since a Memorandum of Understanding was signed last week by Iran and the US. As part of the deal, Tehran agreed that it would make its best efforts to ensure full freedom of navigation was restored to the strait and no fees or tolls would be imposed for a minimum of 60 days.

But the Islamic Revolutionary Guards Corps on Thursday rejected the coordinates of two new temporary shipping evacuation lanes announced by the UN’s International Maritime Organisation in conjunction with Oman.

A pre-existing transit separation scheme (TSS) route remains impassable due to mines. The International Maritime Organization (IMO) proposed two routes, one to the north of the TSS in mined Iranian sovereign waters, and another that was much more passable to the south in Omani waters.

The IMO and Oman had advised that the evacuation of hundreds of ships, some which have been trapped for months, had to be coordinated with both organisations so that transit days and waiting areas could be allocated. The statement issuing the coordinates was given by the Oman National Hydrographic Office, but it appeared from the IRGC’s negative reaction that it did not have Iran’s agreement.

The IRGC force described any alternative transit routes as “unacceptable and completely dangerous”.

“Traffic of vessels outside the official routes is prohibited, and we warn against any traffic outside the communicated routes,” it said.

The statement further emphasised that coordination with the IRGC Navy was “mandatory” for any transit through the strategic waterway.

The strait has proved to be Iran’s key negotiating lever, and it does not want to weaken that lever while bargaining is still under way on lifting US sanctions, asset relief and the future of its nuclear programme.

The speaker of Iran’s parliament and its chief negotiator, Mohammad Ghalibaf, said the chokepoint would not return to the status it enjoyed prior to 28 February, the date of the first combined US-Israeli attack on Iran.

“Everyone should know that the administration of the strait of Hormuz will never go back to the way it was before the war,” Ghalibaf said.

Lebanon, along with the strait, has emerged as the stumbling block for US-Iran talks which are meant to lead to a permanent peace after 60 days of talks. Iran has demanded that Israeli troops withdraw from southern Lebanon, where they occupy more than 600 sq km of land.

Israeli and Lebanese officials denied on Thursday that there had been any Israeli withdrawal from southern Lebanon, pushing back on a statement from a US official who said Israel had called back some troops in a gesture of goodwill towards the Lebanese government.

In recent weeks, Lebanon and Israel have been discussing a phased withdrawal of Israeli troops. The Lebanese army would take control of the vacated areas to prevent Hezbollah from re-entering them and also to destroy any facilities belonging to the armed group.

Israeli government spokesperson David Mencer said on Thursday that any “redeployment” of the Israeli military in southern Lebanon would only come after Hezbollah was disarmed. A day earlier, Israel’s defence minister said Israel would not withdraw from Lebanon.

Israel’s bombing of Lebanon has repeatedly proved an obstacle to US-Iran talks, with a flareup in fighting last week prompting Iran to threaten the closure of the strait.

A ceasefire brokered over the weekend has largely stopped the fighting in Lebanon, although Israeli troops have continued to carry out airstrikes and shoot at cars in areas close to the areas they occupy in southern Lebanon. On Thursday, an Israeli drone strike on a car killed three people in south Lebanon.

The US secretary of state, Marco Rubio, said that Israel and Lebanon were making progress on their talks, telling reporters in Bahrain on Thursday that the two countries were “very close” to making a commitment of intent.

Since the calming of fighting in Lebanon, diplomatic attention has returned to the strait of Hormuz.

In a joint statement, the foreign ministries of Iran and Oman agreed to set up a working party on the future administration of the strait.

But Oman is eager that any proposal complies with Article 43 of the United Nations Convention on the Law of the Sea. Oman also believes that cooperation with the IMO humanitarian rescue mission makes it more likely that an agreement can be reached on a new long-term system.

Gulf States and western countries have been warning Iran and Oman not to try to impose fees for services or tolls, which they insist would be in breach of the fundamental principles of the law of the sea.

Oman, unlike Iran, is a full signatory to the UNCLOS, the treaty enshrining the law of the sea, and insists its scheme would only seek voluntary contributions linked to environment and safety services.

In recent days, a stream of diplomats have been to Muscat to hear Oman’s thinking, and whether it believes Iran’s plans are either lawful or desirable.

Tanker Trackers estimated that Iran has exported 40m barrels of crude oil since 15 June, of which half was on Friday last week.

Arab States including Saudi Arabia and Qatar are strongly opposed to tolls, but some Saudi diplomats appear open to paying fees so long as it can be proven it is lawful, and not extortionate.