Iran struck a vessel in the Strait of Hormuz on Thursday, dealing a blow to efforts to restore maritime traffic through the critical waterway and threatening to undermine peace negotiations with the United States.

The attack came just hours after Iran’s Islamic Revolutionary Guard Corps (IRGC) warned ships that they must coordinate with its navy and travel through a designated route in Iranian waters. Under a preliminary agreement reached last week, the U.S. and Iran had reopened the Strait toll-free for 60 days, prompting a rush of vessels to transit the corridor. Many ships had been using an alternative route along the Omani coast, which the Iranian navy on Thursday declared “unacceptable and extremely dangerous”.

“We warn all vessels to strictly refrain from any movement outside the designated routes,” the navy said in a statement carried by the IRGC-linked Tasnim news agency.

Following the strike—first reported by the Wall Street Journal—the Persian Gulf Seaways Management Organization, a body recently created by Tehran to oversee the Strait, warned that “the consequences of traveling on unauthorized routes will be the responsibility of the owner, operator, and commander of the vessel”.

Iranian and U.S. officials later confirmed to the New York Times that the strike was Iranian, though Tehran has not publicly claimed responsibility. The attack has revived fears that the shipping disruptions that roiled global trade for months and sent oil prices soaring are not yet over, despite President Donald Trump’s assurances that the Strait is fully open. Brent crude briefly jumped more than 2% to around $75.50 a barrel on Thursday before falling about 2% in early Friday trading to $74.03. U.S. West Texas Intermediate saw a similar spike before sinking more than 2% to $70.38 a barrel on Friday.

The United Kingdom Maritime Trade Operations organization reported that a cargo vessel transiting 7.5 nautical miles southeast of Dahit, Oman, was struck by an “unknown projectile” that damaged its bridge. No casualties were reported. A U.S. official told the Times that the vessel was hit by a drone. The Journal identified the ship as the Ever Lovely, a Singapore-flagged vessel owned by Taiwan-based Evergreen Marine.

The ship had been stuck in the gulf for more than 100 days, had loaded cargo in Iraq, and attempted to cross the Strait on Thursday morning following the route designated by the U.N.’s International Maritime Organization (IMO) along the Omani coast. Passengers told the Journal there had been no warning from the Iranian navy.

“The situation underscores the importance of clear and unambiguous agreements between the U.S. and Iran regarding a resumption of maritime traffic through the Strait. The wording of the U.S.-Iran [memorandum of understanding] is currently not sufficiently clear,” Jakob Larsen, chief security officer at BIMCO, the world’s largest shipping association, said in a statement on Thursday.

The MOU states that Iran will “conduct dialogue” with Oman to “define the future administration and maritime services in the Strait of Hormuz”. While the Trump administration has insisted it will not allow Iran to charge tolls or fees for transit, analysts have noted that the language of the MOU leaves the issue unresolved.

An Iranian official told the Times that Oman has been in discussions with Iran to create a management system for the Strait while facing U.S. pressure to reject monetization of the waterway. “Oman is in a tight spot,” the official said, “because it cannot provide security guarantees to vessels without Iran on board”.

In light of the attack, the IMO halted its operation to escort hundreds of stranded ships out of the Persian Gulf. More than 11,000 seafarers have been stuck in the region, unable to leave out of fear of attack. Fourteen seafarers were killed in attacks on commercial vessels over the course of the war.

“I have always reiterated that the safety of the seafarers remains paramount. Therefore, to ensure a coordinated approach and navigational safety, the evacuation plan will be paused until further clarity is obtained,” IMO Secretary-General Arsenio Dominguez said in a statement on Thursday. Dominguez said the ship that was attacked was not part of the agency’s evacuation. The escort mission had begun on Tuesday after the agency said it had secured safety guarantees and was working in close cooperation with Iran.

Shipping through the Strait surged in recent days after the MOU was signed, as companies hoped to take advantage of the two-month toll-free period to export oil and liquefied natural gas. Around 70 vessels, including 29 tankers, transited the Strait on Wednesday—the busiest day since March 1, though still below the roughly 130 ships that passed through daily before the war. Analysts have said energy prices will gradually ease in the weeks after the MOU, but it could take months before they return to pre-war levels, and attacks on vessels could extend that timeline further.

American and Iranian negotiators have met to flesh out the terms of a final deal, and Secretary of State Marco Rubio said on Wednesday that technical talks will begin on June 30, with working groups focused on Iran’s nuclear program and sanctions. Rubio met with Gulf Arab leaders in Bahrain on Thursday to assuage their concerns over certain MOU terms, including the ambiguous language around management of the Strait.

“The reality of it is that no country on Earth has a right to charge for the use of international waterways, and that will never be an acceptable condition of any deal,” Rubio said. Earlier this week, after a meeting between Iran’s parliamentary speaker and Oman’s foreign minister, Oman said Iran had “affirmed commitment to international law and toll-free safe passage”. But Thursday’s attack complicates that promise, and what comes after the 60-day period remains uncertain. Tehran has repeatedly said it wants control over the Strait, a portion of which runs through its territorial waters, and has floated the idea of charging service fees.

On Tuesday, Trump insisted on Truth Social that the Strait is open and warned he could reimpose a U.S. naval blockade on Iranian ports if necessary. He also sought to allay concerns over economic concessions to Iran, claiming that “The Money and/or Sanctions that the U.S. Treasury is releasing goes into escrow, controlled by the U.S.A., and will be used for the purchase of food and medical supplies, exclusively from the United States, including Corn, Wheat, and Soybeans from our great American Farmers”. But Iran rejected that assertion.

“With regard to Iran’s released assets, we will make decisions in whatever way serves the country’s interests and is most beneficial,” foreign ministry spokesperson Esmaeil Baghaei told media.

“Concerning the purchase of goods, our Ministry of Agriculture and other relevant authorities will decide based on both price and quality. Therefore, there are no restrictions in this regard”.

“It is interesting to us that the philosophy and objective of the war, which they previously declared to be the destruction of Iranian civilization and the collapse of Iran, has now been reduced to making American farmers richer,” Baghaei added.

Trump also said in his Tuesday post that Iran had “fully and completely agreed to highest level Nuclear inspections long into the future (Infinity!!!) … If they did not agree to this, there would be no further negotiations!”

Vice President J.D. Vance told reporters on Monday that Iran had agreed to allow inspectors from the U.N.’s nuclear watchdog, the IAEA. But Iran disputed the claims, with Baghaei telling reporters that Iran had made “no new commitments”.

The IAEA has had limited access to inspect Iran’s nuclear sites since the U.S. and Israel bombed Iran’s nuclear facilities last June.

Tensions also remain over Israel’s offensive in Lebanon, which has killed more than 4,000 people, according to Lebanon’s health ministry. Iran has repeatedly said any peace deal must include Lebanon, a point also stated in the MOU. Nevertheless, Israel, which has criticized the MOU, has ramped up its attacks on Lebanon.

The Trump administration has appeared to grow frustrated with Israel; Rubio is skipping Israel on his current Middle East tour, and Vance said last week that Israel cannot “just kill your way out of solving every single national security problem that you have”.