Iran is to free seven out of 23 crew members from the detained British-flagged oil tanker Stena Impero, according to Iranian state TV.
Abbas Mousavi, a spokesman for Iran’s foreign ministry, told the broadcaster they were being freed on humanitarian grounds and would be allowed to leave the country soon.
Stena Bulk chief executive Erik Hanell said: “We are very pleased that for seven crew members their ordeal may soon be over, and they may return to their families, however, we cautiously await official confirmation of their release date.
“We view this communication as a positive step on the way to the release of all the remaining crew, which has always been our primary concern and focus.”
He added the remaining 16 crew members would remain on board the ship to safely operate the vessel.
The Swedish-owned Stena Impero was detained by Tehran on 19 July in the Strait of Hormuz for alleged marine violations, two weeks after Britain detained an Iranian tanker – the Adrian Darya 1 – off the territory of Gibraltar.
The Iranian vessel, previously known as the Grace 1, was released in August amid speculation that it planned to transport its cargo to Syria, in breach of European Union sanctions.
It is carrying 2.1 million barrels of Iranian crude worth about $130m (£108.4m).
Iranian officials have not revealed who bought the ship’s cargo, only confirming that it has been sold.
The vessel switched off its Automatic Identification System (AIS) – its tracking beacon – on Monday afternoon, according to the ship-tracking website MarineTraffic.com.
At its last report, the vessel, which is being pursued by the US, was 45 nautical miles (83km) off the coast of Lebanon and Syria, heading north.
US Secretary of State Mike Pompeo said intelligence suggested the vessel was heading to the Syrian port of Tartus – a short distance from its last-known position.
The US alleged in federal court that the ship is owned by Iran’s Revolutionary Guard, a paramilitary organisation answerable only to Supreme Leader Ayatollah Ali Khamenei.
America recently described the Revolutionary Guard as a terrorist organisation, giving it greater power to pursue seizing its assets.
Bob Sanguinetti, chief executive of the UK Chamber of Shipping, also welcomed the release of the Stena Impero crew, and added “but this must be followed by the immediate release of the vessel and the rest of the crew”.
“The ship was in international waters when it was detained and was in full compliance with all navigation and international regulations,” he said.
“The chamber will continue to work with the UK government to ensure the free passage of ships through the Strait of Hormuz.”
The Strait of Hormuz is a vital shipping lane for oil and gas.
Meanwhile, Iranian President Hassan Rouhani warned Tehran would further cut its commitments under the beleaguered 2015 nuclear deal.
US President Donald Trump withdrew America from the Obama-era accord last year and reimposed sanctions on Iran.
Iran’s vital crude oil sales have plummeted by more than 80% as a result.
In May, Mr Rouhani said Iran would pull out of some of its commitments under the deal and increase the level of its uranium enrichment if new and better terms with world powers were not reached in 60 days.
However, on Wednesday, he gave the remaining signatories of the nuclear deal – Britain, China, the European Union, France and Germany – another two months to save the pact.
At the same time, state television said Iran had rejected the EU countries’ offer of $15bn (£12.3bn) in credit lines until year-end if Tehran returned to full compliance.
Instead, Iran would continue to breach the deal and accelerate its nuclear activity.
“The third step [in reducing Iran’s commitments] will be the most important one and it will have extraordinary effects,” Mr Rouhani said.
The 2015 nuclear deal limits Iran to enriching uranium to 3.67%, which can fuel a commercial nuclear power plant.
Weapons-grade uranium needs to be enriched to around 90%.
However, once a country enriches uranium to around 20%, scientists say the time needed to reach 90% is halved. Iran has previously enriched to 20%.
The European powers have been working to save the nuclear deal to bring Iran back into the international fold and prevent it from developing a nuclear bomb.
Iran has repeatedly said its nuclear programme is for electricity generation and other peaceful purposes.
Iran is to free seven crew members from the detained British-flagged oil tanker Stena Impero, according to Iranian state TV.