A United Nations agency paused the evacuation of ships through the strait of Hormuz on Thursday after the British military said a vessel was hit by a projectile off the coast of Oman following the passage of several tankers that used a route backed by the UN.

The head of the UN’s International Maritime Organization said the plan to move stranded ships out of the Persian Gulf through the strait will be on hold until the agency can confirm safety guarantees for the ships on the evacuation list and in the region.

It was unclear who launched the projectile or the type of vessel that was targeted. The report of a strike came hours after Iran threatened vessels to stop using the route through the strait without Tehran’s permission.

The vessel that was attacked was not part of the evacuation effort, said Arsenio Dominguez, the UN agency’s secretary-general.

After reports of the attack, Iran’s Persian Gulf strait authority – a new government agency established to control shipping in the strait – wrote on X that transit outside its own designated routes “will not be covered by the guarantee of safe passage”.

The UK Maritime Trade Operations centre said the vessel sustained damage, but it reported no injuries or environmental effects from the attack off the coast of Oman.

The opening of an alternative passage through the vital waterway would relieve pressure on the world economy and remove Iran’s main source of leverage in ongoing peace talks with the United States. The US secretary of state, Marco Rubio, on a visit to the Gulf to reassure American allies, said Washington was committed to the new route and ensuring that ships are able to transit the strait.

“If that stops, then we’re going to have a problem,” Rubio said Thursday before the report of the strike on the ship.

Traffic through the strait increased in recent days but was still well below prewar levels. Oil on Thursday briefly dipped below its last prewar price of just under $73 per barrel, a sign that the market believes the situation is improving.

The US and Iran are still debating terms of an interim peace deal, including issues such as getting ships through the narrow mouth of the Persian Gulf and addressing the future of Iran’s stockpile of highly enriched uranium.

Under the memorandum of understanding signed last week, the US and Iran have 60 days to iron out the details. As talks are held behind closed doors, US President Donald Trump and Iranian leaders have seemed to negotiate in public, trading threats and claiming concessions the other side denies.

Meanwhile, a flare-up of fighting in Lebanon between Israel and Iranian-backed Hezbollah militants threatened the wider truce. Lebanon says five people have been killed by Israeli strikes over the past two days. Iran says the tentative deal to end the war would require Israel to withdraw from Lebanon – a condition Israel has rejected.

Oil tankers, led by the Stoic Warrior vessel, sailed along the United Arab Emirates and then Oman early Thursday, passing by Oman’s Musandam peninsula fairly close to the shore. The route was laid out by Oman and the International Maritime Organization.

North of the route is a corridor in the centre of the strait where ships moved freely before the war, transporting about a fifth of the world’s oil and natural gas.

Iran said it mined that passage after the US and Israel attacked it on 28 February. At least one mine has been sighted there.

Though some ships had been getting out of the strait with US military support, the UN agency’s effort was the latest to free trapped vessels. The shipping company Maersk said its container ship, the Maersk Baltimore, and another chartered vessel made it out on Thursday.

Last week, 125 vessels crossed the strait, up from 33 the week before, according to marine data and analysis firm Lloyd’s List Intelligence.

According to S&P Global, there were 78 transits on Wednesday, the most since the war began, but still below the daily prewar average of 130 or more.

The naval arm of the Islamic Revolutionary Guard Corps (IRGC) issued a warning on Thursday against using the new route.

In a statement carried by Iran’s state-run IRNA news agency, naval officials said the route was established without notice or coordination with Iran, calling it “unacceptable and completely dangerous”.

“The only authorised route for passing through the strait of Hormuz is the one declared by the Islamic Republic of Iran,” the Iranian force said. “Vessel traffic outside these routes is extremely dangerous and prohibited.”

“Violators will be dealt with,” it added, without elaborating.

On Wednesday, the IRGC threatened one tanker over the radio, with a soldier warning, “You are in range of my missiles and maybe (I) fire on you,” according to the private security firm Ambrey.

Rubio met foreign ministers from the six-nation Gulf Cooperation Council to assure them that their interests would be protected in any agreement with Iran.

Those countries, including major energy producers reliant on the strait for exports, came under attack by Iran after the start of the war.

“There is no part in this deal that’s undertaken that in any way undermines the security, the stability or the prosperity of any of our partners in the Gulf region,” Rubio said at the meeting in Bahrain.

Bahrain’s foreign minister, Abdullatif bin Rashid al-Zayani, said the agreement brought a glimmer of hope but stressed that it was “critically important that Iran adheres to its obligations.”