TEHERAN • A British-flagged tanker that Iran seized in July is now free to leave, Teheran has said, more than a month after the British authorities released an Iranian tanker detained off Gibraltar.

The news offered a rare hint of easing tensions for Iran, at a time when the country has been in an escalating cycle of confrontation with its Persian Gulf neighbours and with the United States - including the shooting down of drones, the seizure of tankers and, most recently, an attack on major oil installations in Saudi Arabia.

Officials of the US and Saudi Arabia, Iran's chief rival in the region, have blamed Teheran for the Sept 14 attack on oil facilities in the kingdom, raising the prospect of retaliatory strikes and even war.

But so far, the only apparent action they have taken against Teheran is a tightening of economic sanctions.

Iran had accused the British-flagged tanker, the Stena Impero, of violating maritime regulations in the Strait of Hormuz, but the seizure on July 19 was widely seen as retaliation for the detention of the Iranian vessel.

The legal proceedings against the Stena Impero have concluded, and Iran has decided to waive alleged violations, an Iranian government spokesman, Mr Ali Rabiyee, said yesterday at a news conference, according to Iranian and Western news agencies that were present.

The ship had not left Bandar Abbas, a port in southern Iran, as of midday, and it was not clear how quickly it would set sail. Mr Erik Hanell, chief executive of the tanker's owner, the shipping company Stena Bulk, told Swedish television station SVT that he hoped it would be a matter of hours.

Iran had detained the 23-member crew along with the ship. It released seven of them earlier this month, but the others have remained with the vessel.

The decision to release the British-flagged ship comes a little more than a week after the attack on the Saudi oil installations.

Iran has denied any responsibility for the attack, a sophisticated operation involving some two dozen drones and cruise missiles. The aerial strikes damaged infrastructure and temporarily cut Saudi oil production in half, sending tremors through world markets, but they caused no reported casualties.

The Houthi rebel faction in Yemen's civil war, a group that is known to use weapons supplied by Iran, has said it carried out the attack against Saudi Arabia, which has staged bombing strikes in Yemen for more than four years, killing thousands of people.

British Prime Minister Boris Johnson said early yesterday that there was "a very high degree of probability" that Iran was responsible for the attack in Saudi Arabia, and he did not rule out British participation in military retaliation.

Iranian Foreign Ministry spokesman Abbas Mousavi later criticised Mr Johnson's comments and said Britain should stop selling arms to Saudi Arabia amid its war in Yemen, the semi-official Isna news agency reported.

In May and June, several tankers operating near the Strait of Hormuz were damaged in what the US said was sabotage by Iranian forces - which Teheran denied. Iran also detained several ships for varying periods of time, notably the Stena Impero.

Analysts have characterised the attacks - whether carried out by Iran or by one of the armed factions it supports in the Middle East - and ship seizures as Teheran's demonstration that it has the power to cut off a large part of the world's energy supplies.

NYTIMES, ASSOCIATED PRESS