The Iran war risked reigniting after the US tried to force open the Strait of Hormuz for commercial shipping, though a ceasefire seemed to be holding Tuesday even after the United Arab Emirates said Iran fired missiles and drones at it.

It is unclear what will follow after an American attempt to end Iran's stranglehold on the strait by creating an "enhanced security area". A prominent Iranian official accused the US of undermining regional security with the effort and warned that Iran will respond.

The US military said two American-flagged merchant ships successfully transited the strait on Monday, but it remained to be seen if any more ships would cross through on Tuesday.

Ship tracking data showed a Panamanian-flagged crude oil tanker heading toward the centre of the strait Tuesday morning after leaving an anchorage in the Persian Gulf, though it was unclear if it would try to pass through. The tanker had a stated destination of Singapore, according to the MarineTraffic ship tracking site.

Iran's effective closure of the strait, through which about a fifth of the world's trade in oil and natural gas typically passes, along with fertiliser and other petroleum-derived products, has sent fuel prices skyrocketing, rattled the global economy, and proved a major strategic advantage in negotiations to end the war.

Breaking that chokehold would ease global economic concerns and deny Tehran a major source of leverage.

But such efforts also risk reigniting the full-scale fighting that erupted when the US and Israel first attacked Iran on Feb 28, prompting it to close the strait.

Iran has said the new US effort is a violation of the fragile ceasefire that has held for more than three weeks.

In a post on X Tuesday, Iran's powerful parliamentary speaker and chief negotiator, Mohammad Bagher Qalibaf, accused Washington of undermining shipping security in the Strait of Hormuz.

Qalibaf warned that a "new equation" in the strait is taking shape. He signalled that Tehran has yet to fully respond to the US attempt to reopen the waterway, saying: "We know full well that the continuation of the status quo is intolerable for America; while we have not even begun yet."

US President Donald Trump on Sunday warned that Iranian efforts to halt passage through the strait "will, unfortunately, have to be dealt with forcefully". He said the US effort to reopen the strait, dubbed "Project Freedom," was intended to aid stranded seafarers on hundreds of ships that have been stuck in the Persian Gulf since the war began.

The US-led Joint Maritime Information Centre advised ships on Monday to cross the strait in Oman's waters, saying it had set up an "enhanced security area".

Adm Brad Cooper, commander of US Central Command, said American forces had successfully opened a passage free of Iranian mines. He said Iran launched multiple cruise missiles, drones and small boats at civilian ships under the US military's protection. US military helicopters sank six of the small boats, Cooper said.

The United Arab Emirates' Defence Ministry said its air defences had engaged 15 missiles and four drones fired by Iran. Authorities in the eastern emirate of Fujairah said one drone sparked a fire at a key oil facility, wounding three Indian nationals. The British military reported two cargo vessels ablaze off the UAE.

Indian Prime Minister Narendra Modi on Tuesday condemned the attacks, saying the targeting of civilians and infrastructure was "unacceptable".

Tehran did not confirm or deny the attacks but early on Tuesday, Iran's Foreign Minister Abbas Araghchi said on X that both the US and the UAE "should be wary of being dragged back into quagmire."

Pakistan, which has been mediating between the US and Iran, and Saudi Arabia both condemned the strikes against the UAE.

Saudi's condemnation, in a statement from its foreign ministry, called on Iran "to cease these attacks, comply with the principles of international law and relevant United Nations Security Council resolutions, and respect the principles of good neighbourliness."

The statement came despite increasingly strained relations between Saudi and the UAE.

Pakistan's Prime Minister Shehbaz Sharif called for the ceasefire to be upheld, and said in a post on X that Pakistan stands firmly with "our Emirati brothers and sisters as well as with the government of the United Arab Emirates at this difficult time".

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.

The US has meanwhile enforced a naval blockade on Iranian ports since April 13, telling at least 49 commercial ships to turn back, according to Central Command. It's also warned shipping companies they could face sanctions if they pay Iran for transit of the strait.

The blockade has deprived Tehran of oil revenue it needs to shore up its ailing economy. US officials have expressed hope the blockade will force Iran to make concessions in talks on its disputed nuclear programme and other longstanding issues.

Iran's latest proposal for ending the war calls for the US to lift sanctions, end the blockade, withdraw forces from the region, and cease 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 apparatus.

Iranian officials said they were reviewing the US response, though Foreign Ministry spokesperson Esmail Baghaei told reporters Monday that changing demands made diplomacy difficult. He did not give details.

Iran has claimed its proposal does not include its nuclear program and enriched uranium - long a driving force in tensions with the US and Israel.

Iran wants other issues resolved within 30 days and aims to end the war rather than extend the ceasefire. Trump expressed doubt over the weekend that the proposal would lead to a deal.