A look back on how the situation escalated to present situation.
Tensions between Iran and the West have escalated since US sanctions on Iranian oil exports took full effect in May and British naval forces seized an Iranian supertanker.
Below is a timeline of recent incidents:
May 2 - The United States, which withdrew from a nuclear accord between Iran and global powers in 2018 and stepped up sanctions on Tehran, ends waivers that had allowed eight countries - China, Greece, India, Italy, Japan, South Korea, Taiwan and Turkey - to continue buying Iranian crude
May 5 - The United States says it is deploying an aircraft carrier strike group and bombers to the Middle East, citing threats from Iran
May 8 - Iran announces it will relax some curbs on its nuclear program, stopping short of violating its 2015 deal with world powers but threatening more action if countries do not shield it from US sanctions
May 10 - The US Maritime Administration warns of possible Iranian attacks on shipping in the Gulf
May 12 - Four ships, including two Saudi oil tankers, are attacked in the Gulf just outside the Strait of Hormuz, a major oil shipping route. US officials pin the blame on Iran, a charge Tehran denies
June 13 - Two tankers are attacked south of the Strait of Hormuz. Washington again blames Iran and Tehran denies any role
June 20 - Iran shoots down an unmanned US surveillance drone.
July 4 - Royal Marines seize Iranian supertanker Grace 1 near Gibraltar on suspicion of violating European Union sanctions on Syria
July 5 - An Iranian Revolutionary Guards commander threatens to seize a British ship unless the Grace 1 is released
July 7 - Iran says it will boost uranium enrichment above a cap set under the 2015 nuclear deal and will reduce its commitments to the pact, drawing a warning from US President Donald Trump and expressions of concern from Germany, France and Britain
July 10 - Royal Navy frigate HMS Montrose issues verbal warnings and aims its guns at boats believed to belong to Iranian Revolutionary Guards which approached BP oil tanker British Heritage at the northern entrance of the Strait of Hormuz
July 18 - The United States says USS Boxer “destroyed” an Iranian drone in the Strait of Hormuz after it threatened the US Navy ship but Iran denies it has lost a drone
July 19 - Gibraltar extends detention of tanker Grace 1 by one month
July 19 - Iran seizes British-operated oil tankers Stena Impero and Mesdar, the latter released after receiving a warning from Iranian authorities