DUBAI, United Arab Emirates (AP) — The U.S. military said Monday that two American-flagged merchant ships had successfully transited the Strait of Hormuz and that Navy guided-missile destroyers in the Persian Gulf were helping to restore shipping traffic. It separately denied Iran's claims to have struck an American Navy vessel.

The announcement came a day after U.S. President Donald Trump announced a new initiative to help guide ships through the critical waterway for global energy. Iran has effectively closed the strait since the U.S. and Israel started the war on Feb. 28, rattling the global economy.

READ MORE: Trump says U.S. will help 'guide' stranded ships from Strait of Hormuz starting Monday

The U.S.-led Joint Maritime Information Center has advised ships to cross the strait in Oman's waters, saying it set up an "enhanced security area." U.S. Central Command did not say when the Navy ships arrived or when the merchant vessels departed.

It was unclear whether shipping companies, and their insurers, will feel comfortable taking the risk given that Iran has fired on ships in the waterway and vowed to keep doing so. Hundreds of ships have been bottled up in the Persian Gulf for weeks.

Iran has said the new U.S. effort is a violation of the fragile ceasefire reached in early April. Its control of the strait has allowed it to inflict pain on the global economy despite being outgunned on the battlefield.

The United Arab Emirates meanwhile issued an emergency missile alert urging residents to immediately seek shelter. It was the first such alert since the ceasefire war went into effect in early April. There were no immediate reports of casualties or damage and an all-clear order was later issued.

U.S. denies Iranian claims to have struck a Navy vessel

Iranian news agencies, including the semiofficial Fars and the Iranian Labour News Agency, had earlier claimed that Iran struck a U.S. vessel near an Iranian port southeast of the strait, accusing it of "violating maritime security and navigation norms." The reports said the vessel was forced to turn back.

The U.S. Central Command said on social media that "no U.S. Navy ships have been struck."

The U.S. military has said the new initiative might involve guided-missile destroyers, more than 100 aircraft and 15,000 service members but has not specified what kind of assistance it would provide.

Trump's announcement that the U.S. would "guide" ships out of the strait warned that Iranian efforts to block them "will, unfortunately, have to be dealt with forcefully."

He described "Project Freedom" in humanitarian terms, designed to aid stranded seafarers, many on oil tankers or cargo ships, who have been stuck in the Persian Gulf since the war began. Crews have described to The Associated Press seeing drones and missiles explode over the waters as their vessels run low on drinking water, food and other supplies.

Iran's state-run IRNA news agency called "Project Freedom" part of Trump's "delirium."

Iran's military command on Monday said ships passing must coordinate with them.

"We warn that any foreign military force — especially the aggressive U.S. military — that intends to approach or enter the Strait of Hormuz will be targeted," Maj. Gen. Pilot Ali Abdollahi told state broadcaster IRIB.

And the United Arab Emirates on Monday accused Iran of targeting a tanker linked to its main oil company with two drones as it passed through the strait. It did not say when the attack took place. No injuries were reported.

The Joint Maritime Information Center urged mariners to coordinate closely with Omani authorities "due to anticipated high traffic volume." It warned that passing close to usual routes, known as the traffic separation scheme, "should be considered extremely hazardous due to the presence of mines that have not been fully surveyed and mitigated."

But the head of security for the Baltic and International Maritime Council, a leading shipping trade group, said no formal guidance or details about the U.S. effort had been issued to the industry. Jakob Larsen questioned whether the effort was sustainable in the long run or envisioned as a more limited operation, and said there is a "risk of hostilities breaking out again" if it goes ahead.

Iran stands firm on its grip of the strait

The disruption of the waterway has squeezed countries in Europe and Asia that depend on Persian Gulf oil and gas, raising prices far beyond the region.

Trump has promised to bring down gas prices as he faces midterm elections this year.

The U.S. has warned shipping companies they could face sanctions for paying Iran for transit of the strait. It has enacted a naval blockade on Iranian ports since April 13, telling 49 commercial ships to turn back, U.S. Central Command said Sunday.

WATCH: Trump rejects Iran's latest proposal as he reviews new military options to relaunch war

The blockade has deprived Tehran of oil revenue it needs to shore up its ailing economy.

U.S. officials have expressed hope that the blockade forces Iran back to the negotiation table.

"We think that they've gotten less than $1.3 million in tolls, which is a pittance on their previous daily oil revenues," U.S. Treasury Secretary Scott Bessent told Fox News on Sunday, adding that Iran's oil storage is rapidly filling up and "they're going to have to start shutting in wells, which we think could be in the next week."

Iran's latest 14-point proposal for ending the war, made public over the weekend, calls for the U.S. lifting sanctions, ending the U.S. naval blockade, withdrawing forces from the region and ceasing all hostilities, including Israel's operations in Lebanon, according to the semiofficial Nour News and Tasnim agencies, which have close ties to Iran's security organizations.

Iranian officials said they were reviewing the U.S. response, though Foreign Ministry spokesperson Esmail Baghaei told reporters on Monday that changing demands, which he did not detail, made diplomacy difficult.

Iran has claimed its proposal does not include issues related to its nuclear program and enriched uranium — long a driving force in tensions with the U.S. and Israel.

Iran's proposal wants other issues resolved within 30 days and aims to end the war rather than extend the ceasefire. Trump on Saturday said he was reviewing the proposal but expressed doubt it would lead to a deal.

Iranian crew was taken off seized tanker

Pakistan said Monday it has facilitated the transfer of 22 crew members from an Iranian vessel seized earlier by the U.S., describing the move as a confidence-building measure as Islamabad attempts to revive talks. Pakistan hosted face-to-face talks last month.

Pakistan's Foreign Ministry said the crew members, who had been aboard the Iranian container ship MV Touska, were flown to Pakistan overnight. They were expected to be handed over to Iranian authorities.

The vessel will be brought into Pakistani territorial waters for necessary repairs before being returned to its original owners, the ministry said, adding that the process is being coordinated with the support of Iran and the U.S.

Metz reported from Ramallah, West Bank. Munir Ahmed contributed from Islamabad, Pakistan.