Iran captures UK tanker: Timeline of Persian Gulf political tensions

The seizure of the Stena Impero tanker in the Strait of Hormuz is the latest episode to contribute to rising tensions between the UK, US and Iran in the region.

After Donald Trump unilaterally withdrew the US from a long term nuclear agreement it had signed with five other world powers, tensions have worsened with Washington.

Iran has refused to negotiate any changes, and has threatened to further break the terms of the agreement if Europe does not help limit the effects of US sanctions. It has also broken restrictions on its production of enriched uranium, used to make reactor fuel but also potentially nuclear bombs.

Tensions between the UK and Iran flared up earlier this month when Royal Marines seized an Iranian tanker which was suspected of breaking European Union sanctions. The UK suspected Grace 1, detained near Gibraltar, was carrying oil bound for Syria.

Foreign secretary Jeremy Hunt said it would be released if Tehran guaranteed its oil would not be given to the country's president Bashar al-Assad's regime.

Here is a timeline of recent incidents involving the three nations:

13 June: Two US oil tankers near the Strait of Hormuz were attacked in an assault that left one ablaze and adrift, with 44 sailors evacuated from both vessels. The US Navy went to assist, with Mr Trump blaming Iran for the incidents.

Iran denied involvement in the tanker attacks and accused the US of promoting an "Iranophobic" campaign.20.

20 June: A US military drone worth $100m (£78m) was downed by Tehran, with Iran's president Hassan Rouhani claiming it had violated their airspace.

The move marked a new high in the rising tensions between the two countries, as Iran's naval commander warned his forces would not hesitate to down more US drones if they entered its airspace.

Mr Trump then pulled back from the brink of retaliatory military strikes on Iran after he was told 150 people could die.

He has since signed an executive order targeting Iran's supreme leader Ali Khamenei and his associates with financial sanctions.

4 July: Royal Marines from 42 Commando were involved in an operation to seize a supertanker off Gibraltar suspected of carrying oil destined for Bashar Assad's Syrian regime. They boarded the ship by descending on ropes from a Wildcat helicopter and by using rigid inflatable boats.

They worked alongside authorities in Gibraltar to detain the Iranian tanker Grace 1, which was believed to be heading to the Banyas refinery in breach of EU sanctions. In response, Iran's revolutionary guard warned a British oil tanker could be seized in retaliation.

10 July: Royal Navy frigate HMS Montrose drove off three Iranian vessels which tried to stop the commercial ship British Heritage.

It is understood the tanker was making passage out of the Gulf through the Strait of Hormuz when the ship was approached by the Iranian vessels. HMS Montrose was nearby and proceeded to come in between.

Warnings were given but no shots were fired. The Iranian vessels then turned around and left.

11 July: Police in Gibraltar said they had arrested the captain and chief officer of the Iranian supertanker Grace 1 in relation to suspected violations of EU sanctions on Syria.

Two days later the force said the captain, chief officer and two second officers of the vessel had been conditionally bailed without charge.

13 July: In a telephone call with Iranian foreign minister Mohammad Javad Zarif, Foreign Secretary Jeremy Hunt offered to facilitate Grace 1's release in return for guarantees from Tehran that it would not breach EU sanctions on the Assad regime in Syria.

15 July: Mr Hunt attended a Brussels meeting of EU foreign ministers on the issue of the Iran nuclear deal. He said there was a "small window" of hope for preventing the international agreement, aimed at stopping Tehran gaining nuclear weapons, from unravelling.

Both he and Tory leadership rival Boris Johnson later ruled out supporting Mr Trump should he pursue military action in the Gulf.

16 July: Ali Khamenei called the seizure of the Grace 1 tanker "piracy" and vowed to retaliate. He said: "God willing, the Islamic Republic and its committed forces will not leave this evilness without a response."

17 July: US officials said they suspected Iran had seized a Panamanian-flagged oil tanker from the United Arab Emirates as it travelled through the Strait of Hormuz. The tanker had turned off its tracker three days before as it entered Iranian waters.

Iran later said its Revolutionary Guard had seized a foreign oil tanker and its crew of 12 for smuggling fuel out of the country.

18 July: Mr Trump said the USS Boxer had shot down an Iranian drone that came within 1,000 yards of the warship and ignored calls to stand down.

Iranian military officials denied one of its drones had been lost in the Strait of Hormuz.

19 July: Two oil tankers are reported to have been seized by Iranian authorities in the Persian Gulf.

The Stena Impero, registered in the UK, was seized by the Iranian Revolutionary Guard in the Strait of Hormuz for "violating international maritime rules", the semi-official Fars news agency said.

A second oil tanker, the Liberia-flagged Mesdar, owned and operated by Glasgow-based firm Norbulk, appeared to veer off course towards the Iranian coast.

The Mesdar's operator said the ship was boarded by armed guards but the crew were left "safe and well" and allowed to continue their voyage.

Jeremy Hunt called the ships' seizure "unacceptable" ahead of attending a meeting of the Government's emergency committee Cobra.

Press Association contributed to this report