A ship has reportedly sunk in a major sea route after an explosion, while other ships have also come under attack.
Iran’s Revolutionary Guards say a container ship hit a mine and sank in the Strait of Hormuz.
They said the ship was using an unauthorised route.
Images released by the Guards show black smoke rising from the ship and dozens of containers floating in the water.
They said the vessel was carrying more than 2,500 containers.
British security says a Singapore-flagged container ship, the GFS Pride, was hit by a projectile on Tuesday and sank.
It is not clear whether the two reports describe the same ship.
Reports also says three other ships were hit that day.
Two kept going, and the fate of the third is unknown.
The UK Maritime Trade Operations Centre says two container ships were hit by projectiles on Tuesday.
Both continued on their way with only minor damage.
It also reported two other attacks that day, on a tanker and a container ship, without saying whether they caused damage.
Iran claims control of the strait, which normally carries about a fifth of the world’s oil and gas.
It often targets ships it says pass without permission.
The US has also imposed a blockade on Iran’s ports.
The tensions began in late February, when US and Israeli strikes hit Iran.