The US Navy has enforced a blockade against ships entering or exiting Iranian ports and coastal areas, seizing two vessels and directing 27 others to turn around or return to an Iranian port.
The blockade, in place since April 13, is being enforced by at least 15 US warships and has been met with criticism from Iran, which has called it illegal and a violation of the ceasefire between the two countries.
US allies have refused to back the blockade, and Iran has warned it will retaliate against the ports of US allies in the Gulf if its own ports are threatened.
The US Navy has boarded two vessels, one off Chabahar Port in the Gulf of Oman and one in the Indian Ocean, and directed 27 others to turn around or return to an Iranian port as of April 21.
The blockade has been enforced using a combination of warships and special operations forces, and has been supported by the US Department of War, which has stated that the warships are positioned in the Gulf of Oman and in the Arabian Sea region.
International maritime law allows warships to approach commercial vessels and conduct a 'right of visit' boarding to verify nationality, check for illicit activity, or enforce blockades during wartime.
The US Navy has also deployed submarines and other warships to support the blockade, and has warned that it will take control of tankers if they attempt to evade the blockade.
Iran has warned that if its ports are threatened, then no ports in the Persian Gulf or Gulf of Oman would remain secure, and has threatened to strike ports in the region in response to the blockade.
