The captain and chief officer of an Iranian oil tanker which was seized by Royal Marines last week, have been arrested by Gibraltar police.
The men, both Indian nationals, were arrested on Thursday afternoon but neither have been charged, a spokesman said.
Royal Marines Commandos boarded the Panamanian-flagged Grace 1, as it passed by Gibraltar, after it was suspected of carrying crude oil to Syria in breach of EU sanctions.
The resulting tensions nearly boiled over Wednesday, when three Iranian vessels tried to impede UK-flagged tanker British Heritage as it made its way through the Strait of Hormuz, ordering it to change course and stop.
Royal Navy frigate HMS Montrose aimed their guns on the Iranian vessels and ordered them to back away, which they did without firing a shot.
The frigate’s Wildcat helicopter was also deployed to ‘buzz’ the Iranian boats by circling close overhead.
‘HMS Montrose was forced to position herself between the Iranian vessels and British Heritage and issue verbal warnings to the Iranian vessels, which then turned away,’ a British government spokesman said in a statement.
Britain has since issued guidance to all its commercial vessels around the Strait of Hormuz, putting them on ‘heightened security’ and telling them to beware of Iranian boats ‘being aggressive’, Sky News reported.
Jeremy Hunt had described the clash in the Strait of Hormuz as a ‘very concerning development’.
He told the BBC: ‘I am very proud of the Royal Navy and the role they played in keeping British assets, British shipping safe.
‘We are continuing to monitor the situation very, very carefully.’
Defence Secretary Penny Mordaunt added: ‘The crew of HMS Montrose yesterday ensured the safe passage of the merchant vessel British Heritage through the Strait of Hormuz.
‘I would like to thank the Royal Navy for their professionalism, which upheld international law and supported freedom of navigation through a shipping channel that is vital to global trade.
‘The UK Government is concerned by this action and we urge the Iranian authorities to de-escalate the situation.’
Iran’s Foreign Minister Mohammad Javad Zarif described the allegation that Iran had sought to block the ship as ‘worthless’.
It came as a deputy commander in Iran’s Revolutionary Guards warned Britain that ‘the enemy will regret detaining our oil tanker’.
The same commander also said that retaliatory actions will be announced against Britain soon, without giving further details.
Iran has threatened to seize a British tanker in retaliation, after the UK stopped one of its vessels – the Grace 1 – off the coast of Gibraltar last week.
About 20 per cent of all oil traded worldwide passes through the Strait of Hormuz from Middle East producers.
Iran has repeatedly threatened to close the shipping lane if it is prevented from exporting its own oil.
US sanctions have largely shut down its oil exports.
Iran’s President Hassan Rouhani said in a cabinet session on Wednesday that Britain would ‘see the consequences’ after the Gibraltar seizure.
In remarks broadcast on Iranian TV, Rouhani said: ‘You (Britain) are the initiator of insecurity and you will realise the consequences later.
‘Now you are so hopeless that, when one of your tankers wants to move in the region, you have to bring your frigates, because you are scared.
‘Then why do you commit such acts? You should instead allow navigation to be safe.’