What is the Strait of Hormuz?
The Strait of Hormuz lies between Oman and Iran. It links the Gulf with the Gulf of Oman to the south, and the Arabian Sea beyond. It is 33km wide at its narrowest point, with the shipping lane just 3km wide in either direction. The United Arab Emirates (UAE) and Saudi Arabia have sought to find other routes to bypass the strait, including building more pipelines.
Why does it matter?
Almost a fifth of the world's oil passes through the strait - some 17.4 million barrels per day (bpd), out of a consumption of about 100 million bpd last year, data from analytics firm Vortexa showed. Opec members Saudi Arabia, Iran, the UAE, Kuwait and Iraq export most of their crude oil via the strait. Qatar, the world's biggest liquefied natural gas exporter, also sends almost all of its gas through the strait.
Any disruption to the oil supply will cause prices to rise and impact consumers.
The United States has imposed sanctions on Iran aimed at halting its oil exports.
Iran has threatened to disrupt oil shipments through the strait if the US tries to strangle its economy .
The US Fifth Fleet, based in Bahrain, is tasked with protecting commercial shipping in the area.
1980-1988 Iran-Iraq war: The two sides seek to disrupt each other's oil exports in what is known as the Tanker War.
July 2010: Japanese oil tanker M Star is attacked in the Strait of Hormuz by militant group Abdullah Azzam Brigades, which is linked to Al-Qaeda.
January 2012: Iran threatens to block the strait in retaliation for US and European sanctions to stop Iran's nuclear programme.
May 2015: Iranian ships seize a container ship in the strait and fire shots at a Singapore-flagged tanker which Teheran says damaged an Iranian oil platform.
May 2019: Four vessels - including two Saudi oil tankers - are attacked off the UAE coast near Fujairah, one of the world's largest bunkering hubs, just outside the strait.