The fragile ceasefire between the United States and Iran has been pushed to the brink after the two sides exchanged fire in the Strait of Hormuz on Thursday, with each accusing the other of firing first in one of the most serious escalations since hostilities between the two countries began in late February.

Iran’s military was first to go public with an accusation, claiming that US forces had violated the ceasefire by targeting an Iranian oil tanker that was moving from Iranian coastal waters toward the strait.

Tehran described it as an act of aggression by what it called the “terrorist and bandit” American military, and said its forces immediately retaliated by launching a barrage of ballistic missiles, anti-ship cruise missiles, and high-explosive drones at US Navy vessels east of the Strait of Hormuz, near Chabahar Port, claiming the strikes caused significant damage to American ships.

The US military offered a sharply different account. US Central Command said its forces intercepted what it described as unprovoked Iranian attacks as three Navy guided-missile destroyers were transiting the strait toward the Gulf of Oman. CENTCOM said it then responded with self-defence strikes, targeting Iranian military facilities it said were responsible for the attacks, including missile and drone launch sites, command and control locations, and surveillance nodes.

The command added that it does not seek escalation but remains ready to defend American forces.

President Donald Trump weighed in on Truth Social, playing down any damage to American assets.

“Three World Class American Destroyers just transited, very successfully, out of the Strait of Hormuz, under fire,” he wrote. “There was no damage done to the three Destroyers, but great damage done to the Iranian attackers. They were completely destroyed along with numerous small boats.” Iran’s state-affiliated media told a different story, with the IRGC-linked Tasnim News Agency reporting that American destroyers were targeted by missiles and suicide drones, and claiming the ships were seen retreating toward the Sea of Oman.

The flare-up comes just weeks after a ceasefire between Washington and Tehran came into effect on April 8, ending nearly six weeks of open warfare that began on February 28 when the US and Israel launched an air campaign against Iran and Israeli forces assassinated Supreme Leader Ali Khamenei. Iran had since blockaded the Strait of Hormuz — a chokepoint through which roughly a quarter of the world’s seaborne oil trade passes — and the US responded in mid-April by imposing a naval blockade on Iranian ports.

Trump had told Congress as recently as last Friday that hostilities with Iran had “terminated,” noting there had been no exchange of fire since April 7.

The renewed fighting threatens to unravel what little diplomatic ground has been gained. Blasts were reported near the ports of Bandar Abbas and Qeshm Island in southern Iran following the exchange, and Iran’s air defences claimed to have shot down two hostile drones over the area. The wider international community is watching anxiously as energy markets brace for the impact of what is increasingly looking like an unravelling peace.