The oil tanker was suspected of carrying crude oil to Syria
Foreign Secretary Jeremy Hunt has said the Iranian tanker detained by Royal Marines near Gibraltar could be released, if the UK is guaranteed the oil is not bound for Syria.
The tanker seized on 4 July was suspected of breaking EU sanctions.
Iran claimed the seizure was “piracy”, and Iranian ships later tried to impede a British tanker, the UK claimed.
After “constructive” talks with Tehran, Mr Hunt said he was encouraged Iran has no desire to escalate the situation.
“I reassured him our concern was destination, not origin of the oil,” he wrote on Twitter, “and that UK would facilitate release if we received guarantees that it would not be going to Syria.”
He added that the foreign minister, Mohammad Javad Zarif, wants to resolve the issue and was “not seeking to escalate”.
Why was the tanker seized?
A team of about 30 British Royal Marines were flown from the UK to Gibraltar to help detain the super tanker and its cargo, at the request of the Gibraltar government, the BBC was told.
Authorities said there was reason to believe the Iranian tanker Grace 1 was carrying crude oil to the Baniyas Refinery in Syria.
The refinery is subject to European Union sanctions against Syria.
How did Iran react?
Iran denied the tanker was bound for Syria and threatened to seize a British oil tanker in retaliation.
Iranian foreign ministry spokesman Abbas Mousavi called the actions a “form of piracy” and called for the ship to be immediately released and allowed to continue its journey.
He was quoted as saying the UK’s ambassador in Tehran, Robert Macaire, had been summoned over the “illegal seizure”.
Mr Mousavi added that “the move indicated that the UK follows the hostile policies of the US, which is unacceptable for the Iranian nation and government”.
Iran has since reiterated calls for the tanker to be released.
An Iranian official, speaking to state news agency IRNA, warned the UK not to get involved in “this dangerous game”.
What happened next?
On 9 July, the UK raised the threat to British shipping in Iranian waters in the Gulf to “critical” – the highest level.
A day later, Iranian boats attempted to impede a British oil tanker in the region, before being warned off by a Royal Navy ship, according to the MoD.
Boats believed to belong to Iran’s Islamic Revolution Guard Corps (IRGC) approached the British Heritage tanker and tried to bring it to a halt as it was moving out of the Gulf into the Strait of Hormuz.
HMS Montrose, a British frigate shadowing the BP-owned tanker, was forced to move between the three boats and the ship, a Ministry of Defence spokesman said.
Iran denied any attempted seizure, with Iranian foreign minister Mohammad Javad Zarif quoted as saying the UK made the claims “for creating tension”.