The Strait of Hormuz, a strategically important waterway for the world's seaborne oil transits, has been at the centre of decades of regional tensions.
Here is some background on the strait, which Iran has repeatedly threatened to close in case of a military confrontation with the US.
- Gateway to the Gulf -
The Strait of Hormuz links the Gulf to the Gulf of Oman and is situated between Iran and Oman.
It is vulnerable due to its narrowness -- some 50 kilometres (30 miles) -- and its depth of no more than 60 metres (200 feet).
The corridor is dotted with sparsely inhabited or desert islands, which are strategically important, notably the Iranian islands of Hormuz, Qeshm and Larak.
Oman's Mussandam peninsula juts out to the Strait of Hormuz towards Iran, separated from the rest of the sultanate by United Arab Emirates territory.
With their back to the UAE coast, the strategic and disputed islands of Greater Tunb, Lesser Tunb and Abu Mussa serve as observation posts of all the Gulf coastline.
Iran under the Western-backed shah gained control of the islands in 1971, as Britain granted independence to its Gulf protectorates and withdrew its forces.
- Oil transit hotspot -
The strait is a vital corridor connecting the petroleum-rich states of the Middle East with markets in Asia, Europe, North America and elsewhere.
According to the Energy Information Administration (EIA), 35 percent of the world's seaborne oil passes through the Strait of Hormuz.
- Zone of tension and conflict -
Iran's Revolutionary Guard, the ideological army of the Islamic republic, controls naval operations in the Gulf and the Strait of Hormuz.
Tehran repeatedly criticises the presence of foreign powers in the region, notably the US Fifth Fleet stationed in Bahrain, and it has threatened to close the strait if it comes under attack.
Oil transit was disrupted in 1984 during the Iran-Iraq war (1980-1988) when more than 500 vessels were destroyed or damaged in a "Tanker War".
In 1988, an Iran Air flight from Tehran to Dubai, via Bandar Abbas, was shot down by missiles fired from a US Navy cruiser patrolling the strait. All 290 people on board were killed.
The crew of the USS Vincennes said they mistook the Airbus for an Iranian fighter.
In April 2015 the Revolutionary Guards boarded and took into custody in the strait a container ship flying the flag of the Marshall Islands.
The following month Revolutionary Guard sailors fired warning shots in an apparent bid to intercept a Singapore-flagged cargo ship in the Gulf.
Also read: Will Iran's military capabilities against Israel last in long-drawn war?
