The US and Iran launched new attacks in the Gulf on Monday as they wrestled for control over the Strait of Hormuz with duelling maritime blockades, shaking a fragile truce.

The fresh volleys of missiles and drones came after US President Donald Trump launched a new effort to ‌get stranded tankers and other ships through the strait, the vital energy-trade chokepoint that has been virtually closed since the US and Israel began attacks on Iran in February, a war that has killed thousands of people across the region.

Before Monday was out, several merchant ships in the Gulf reported explosions or fires, the US said it had destroyed six small Iranian military boats, and an oil port in the United Arab Emirates, which hosts a large US military base, was set ablaze by Iranian missiles.

Trump gave scant details about his new effort, which he called “Project Freedom,” to help stuck ships to travel through the strait when he announced it on social media, two days after a legal deadline under US law had passed for him to get authorization from Congress for the war. Trump told Congress the war was “terminated” and the deadline was moot, a claim disputed by some lawmakers.

It was the first apparent attempt to use military force since last month’s ceasefire announcement to unblock the world’s most important energy shipping route, which Iran’s Islamic Revolutionary Guard ⁠Corps has said can only happen with its permission. The cost of shipping insurance has also rocketed. For weeks, the US Navy has blockaded Iran’s trade by sea, which Iran says is itself an act of war.

But Trump’s latest move, at least initially, appeared to have backfired, bringing no surge of merchant ship traffic while provoking a promised show of force from Iran, which has threatened to respond to any escalation with new attacks on its neighbours hosting US soldiers. Major shipping companies said they were likely to wait for an agreed end to hostilities before trying to cross the strait.

Iran’s Foreign Minister Abbas Araqchi said Monday’s events showed there was no military solution to the crisis. He said peace talks were progressing with Pakistan’s mediation while warning the US and the UAE against being drawn into a “quagmire by ill-wishers.”

“Project Freedom is Project Deadlock,” he wrote on social media.

Nonetheless, the US military said two US merchant ships made it through the strait, without saying when, with the support of Navy guided-missile destroyers. While Iran denied any crossings had taken place in recent hours, Maersk said the Alliance Fairfax, a US-flagged ship, exited the Gulf via the Strait of Hormuz accompanied by the US military on Monday.

The commander of US forces in the region said his fleet had destroyed six small Iranian boats, which Iran also denied. Admiral Brad Cooper said he “strongly advised” Iranian forces to keep clear of US military assets carrying out the mission.

Iranian authorities released a map of what they said was an expanded sea area now under their control, extending far beyond the strait to include long stretches of the UAE’s coastline.

South Korea reported one of its merchant ships, HMM Namu, in the strait suffered an explosion and fire in its ‌engine room, though no ⁠one aboard was hurt, and a spokesman said it was unclear if the fire was caused by an attack or originated internally.

The British maritime security agency UKMTO reported two ships had been hit off the coast of the UAE, and the Emirati oil company ADNOC said one of its empty oil tankers was hit by Iranian drones.

Iran sets UAE oil port ablaze

After reported drone and missile attacks inside the UAE throughout the day, including one that caused a fire at Fujairah, an important oil port, the UAE said Iranian attacks marked a serious escalation and it reserved the right to respond. Fujairah lies beyond the strait, making it one of few export routes for Middle East oil that does not require passing through it.

Its government also said that it was implementing remote learning for school students for safety reasons.

Iran’s state television network said military officials had confirmed they attacked the UAE in response to ⁠the “US military’s adventurism.”

Earlier, Iran said it had fired on a US warship approaching the strait, forcing it to turn around. An initial Iranian report had said a US warship was struck, but the US denied this and Iranian officials later described the fire as warning shots.

Reuters could not independently verify the full situation in the strait on Monday as the warring sides issued contradictory statements.

Oil prices jumped more than 5% in volatile trade on reports of the increased Iranian attacks.

Iran’s unified command has told commercial ships and oil tankers that they needed to coordinate with its armed forces.

“We warn that any foreign ⁠armed forces, especially the aggressive US Army, will be attacked if they intend to approach and enter the Strait of Hormuz,” it said.

The US and Israel suspended their bombing of Iran four weeks ago, and US and Iranian officials held one round of face-to-face peace talks. But attempts to set up further meetings have failed.

Iranian state media said on Sunday that the US had conveyed its response to a 14-point Iranian proposal via Pakistan, and Iran was reviewing it. Neither side gave details.

The Iranian proposal would postpone discussion of Iran’s nuclear energy and research ⁠programs until after an agreement to end the war and resolve the standoff over shipping. Trump said over the weekend he was still studying it but would probably reject it.

The latest US intelligence shows limited damage to Iran’s nuclear program, which Iran says is a purely peaceful civilian nuclear program, since the war began, officials told Reuters. Iran’s nuclear facilities were bombed by the US and Israel in attacks last year. Trump wants to remove Iran’s stockpiles of enriched uranium to prevent Iran from processing it further to the point where it could make a nuclear weapon.