DUBAI, United Arab Emirates (AP) — 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 U.N.

WATCH: U.S. and Iran at odds over nuclear inspections, Strait of Hormuz fees

The head of the 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 United Kingdom Maritime Trade Operations center said the vessel sustained damage, but it reported no injuries or environmental impact in 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. U.S. Secretary of State Marco Rubio, on a visit to the Gulf to reassure American allies, said Washington was committed to the new route and making sure ships were able to transit the strait.

"If that stops, then we're going to have a problem," Rubio said earlier Thursday.

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 was improving.

The U.S. and Iran are still debating terms of an interim peace deal — from getting ships through the narrow mouth of the Persian Gulf to the future of Iran's stockpile of highly enriched uranium.

Under the memorandum of understanding signed last week, the U.S. and Iran have 60 days to iron out the details. As talks are held behind closed doors, U.S. 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.

More ships are passing through the strait, but far fewer than before the war

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, a U.N. agency.

North of the route is a corridor in the center of the strait where ships had moved through freely before the war, transporting about a fifth of all the world's oil and natural gas.

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

Though some ships had been getting out of the strait, with U.S. military support, the U.N. agency's effort is 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, Wednesday saw 78 transits, the most since the war began, but still below the daily prewar average of 130 or more.

"Opportunistic operators — and there are many of them — emboldened by the lower transit risk, or at least the perceived lower transit risk, have begun chasing the backlog of trapped cargoes," said Richard Meade, editor-in-chief at Lloyd's List.

Iran says the new shipping route is 'unacceptable'

The naval arm of the Revolutionary Guard issued a warning Thursday against using the route, carried by Iran's state-run IRNA news agency.

It said the new route was established without notice or coordination with Iran, calling it "unacceptable and completely dangerous."

"The only authorized 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 Guard 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 says the U.S. will ensure there are no tolls on ships

Rubio met with 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.

WATCH: Rubio says 'no country' can charge tolls in Strait of Hormuz

"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, home to the U.S. Navy's 5th Fleet.

Bahrain's Foreign Minister Abdullatif bin Rashid al-Zayani thanked the U.S. for its support, saying that because of the agreement, "today we see a glimmer of hope for our region" but stressed that it was "critically important that Iran adheres to its obligations."

Lebanon remains a flashpoint

A lull in fire between Israeli forces and Hezbollah that started Sunday began to show cracks after Israel said it targeted Hezbollah militants.

Lebanon's health ministry said Thursday that three people were killed by an Israeli strike on a car in southern Lebanon.

Hezbollah has called the recent strikes a ceasefire violation but has not retaliated. There was no immediate comment from the Israeli military on the latest strike, which came as Lebanese and Israeli officials were in Washington discussing a proposed phased withdrawal of Israeli troops from southern Lebanon.

Israel's military said Thursday that a reservist soldier was killed and another hurt in southern Lebanon.

Over 4,000 people in Lebanon have been killed in Israeli strikes since the latest Israel-Hezbollah war began in March, when the Lebanese militant group fired at Israel. At least 37 Israeli soldiers have been killed in Lebanon or northern Israel during the fighting.

Lee reported from Manama, Bahrain. Associated Press writers David McHugh in Frankfurt, Germany, and Julia Frankel in Jerusalem contributed to this report.