Iran Asserts Authority Over Strait of Hormuz After Attacking Cargo Ship

President Trump said on Friday that Iran’s attack on a container ship in the Strait of Hormuz a day earlier was a “foolish violation” of the fragile cease-fire between the two countries, though he did not say how or whether he would respond.

In a post on social media, Mr. Trump said Iran had launched at least four one-way-attack drones, one of which hit the upper deck of a “of a large and very expensive Cargo Carrying Ship,” adding that the United States had knocked down three other drones. He added that the ship, though damaged, was able to continue on its way.

Mr. Trump’s comments came after Iran reaffirmed its claim to being a central authority in managing marine traffic through the strait.

The strike on the vessel, the Ever Lovely, a container ship that was passing near the Omani side of the strait, appeared to be the first known Iranian attack on a commercial vessel since the signing of a preliminary peace agreement between Tehran and Washington last week. It laid bare the challenges to restoring prewar levels of traffic through the strait, a crucial conduit for oil and gas shipping.

Although the United States and Iran have agreed to restore access to the strait — with President Trump declaring the waterway open to unrestricted navigation — the preliminary accord does not stipulate exactly how that should happen.

The Iranian Foreign Ministry said in a statement on Friday, carried on state media, that the strait lay within Iranian and Omani waters, and cited a section of the U.S.-Iran deal that Tehran says allows it to manage marine traffic in the strait.

The agreement says that Iran would “make arrangements using its best efforts” for the safe passage of commercial vessels. That wording is vague, leaving room for differing interpretations, according to Jakob Larsen, chief security officer at BIMCO, a global shipping association.

Mr. Larsen said that some shipping companies, and their insurers, might conclude after the Thursday attack that the situation was too risky to proceed with plans to pass through the strait. “There are real fears that hostilities will break out again,” he added.

The strike on the container ship came hours after Iran, demonstrating its hold over the strait, warned that the only way through was via its waters. Many ships, like the Ever Lovely, had been using a U.S.-backed route on the southern side of the strait, hugging the Omani coast.

Iran’s deputy foreign minister, Kazem Gharibabadi, wrote on social media on Friday that safe passage through the strait was “not guaranteed under vague arrangements, parallel routing systems or decision-making processes that exclude Iran as a coastal state.”

Oil markets largely shrugged off the escalation. Prices rose after the strike, but soon reversed as the continued movement of tankers appeared to ease concerns about supply disruptions. Brent crude, the global benchmark, at one point on Friday dropped below $72 a barrel, a level not seen since before the outbreak of war.

Mr. Trump’s comments on social media Friday were his first on the attack. Over the past week, he has made sporadic posts about the Strait of Hormuz, including a declaration that there would not be tolls for passage through the waterway unless they were imposed by the United States.

Iran has discussed with Oman the idea of charging passing ships service fees, a proposal that has drawn the ire of Mr. Trump.

The attack came shortly after Secretary of State Marco Rubio left the Persian Gulf, where he had met with foreign ministers from the Gulf Cooperation Council as he sought reassure regional allies about the preliminary deal with Iran.

In a joint declaration after the meeting, the United States and the Gulf countries in that organization called for “free, unconditional and unrestricted navigation” through the strait and rejected tolls, fees or attempts by any country to assert control over the waterway.

The attack prompted the International Maritime Organization, a United Nations agency, to suspend an effort to help hundreds of stranded vessels leave the Persian Gulf. At least two tankers turned around after Iran’s warning earlier that day, according to Lloyd’s List Intelligence, while the number of ships passing through the strait fell to 54 on Thursday from 73 a day earlier, according to Kpler, a maritime data firm.

Arsenio Dominguez, Secretary General of the I.M.O., said that 115 vessels, with about 2,500 seafarers, had been evacuated since Tuesday. Even though the evacuation program was suspended, some vessels were still transiting via the strait’s southern route, he said.

Mr. Dominguez said the evacuations would restart once the agency had guarantees that no more ships would be attacked, and that they were still investigating the circumstances around the strike against the vessel that was attacked. He said this vessel had passed through the Strait of Hormuz without coordinating with the International Maritime Organization.

Leily Nikounazar, Erica L. Green and Farnaz Fassihi contributed reporting.