Iran denied involvement in the tanker attacks and accused America of promoting an "Iranophobic" campaign.
20 June: An American military drone worth $100 million (£78 million) 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 al-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 European Union sanctions. In response, Iran's revolutionary guard warned a British oil tanker could be seized in retaliation.
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.
The UK government announced it would send a second warship to the Gulf amid escalating tensions with Iran. HMS Duncan, a Type 45 destroyer, is joining HMS Montrose, which is due to go in for "pre-planned maintenance" while continuing its deployment.
UK Foreign Secretary Jeremy Hunt says Britain will release the Grace 1 tanker, as long as the cargo does not break EU sanctions and end up in Syria.
What is the situation as it stands?
Tensions between the US and Iran have ratcheted up several notches in recent weeks, with Washington dispatching warships and bombers around the Persian Gulf, and Tehran announcing it would break uranium stockpile and enrichment limits set by its nuclear deal with world powers.
These increased strains come a year after President Trump withdrew from Iran's 2015 nuclear accord with world powers and restored crippling sanctions. In turn, this prompted Iran to say it would not negotiate another deal with Washington.
Its size belies its importance as one of the most strategic waterways in the world, linking the Middle East's crude oil producers with key markets around the globe.
The Strait falls between the southern coast of Iran and the most northerly tip of Oman, a distance of around 20 miles at these pinch-points.
It has two shipping lanes, each around two miles wide. Between one-fifth and one-sixth of the world's oil moves through the strait - around 17 million barrels per day - a significant quantity of the valuable commodity.
Any impasse on oil leaving the Strait could have wide-ranging consequences - including soaring prices and disruption to world supplies.
At the moment, no. There is already an undisclosed number of British service personnel in the Middle East, predominantly from the Royal Navy. There is a joint base at Duqm in Oman, with a Combined Maritime Forces base in Manama, Bahrain.
HMS Montrose has been in the region since April as part of a three-year deployment supporting counter-terror and anti-smuggling work. The Royal Navy has had a presence in the region for more than 30 years following the Iran-Iraq war in 1980 in what is known as Operation Kipion.
Ships from both the Royal Navy and Royal Fleet Auxiliary have been on patrol in the Gulf for 24 hours a day, seven days a week and 365 days a year, according to the Royal Navy.