Iran will close parts of the strategic Strait of Hormuz for "safety" measures during military drills by its Revolutionary Guards, state TV reported on Tuesday.
"Parts of the Strait of Hormuz will be closed in order to respect the principles of safety and navigation," said a state TV journalist, reporting from a site near the drills, which began on Monday.
He said the partial closure would last for "a few hours".
On Monday, the Islamic Revolutionary Guard Corps began a series of military exercises to prepare against "potential security and military threats" in the strait.
The duration of the war games was not specified.
The drills took place after the United States deployed a large naval force to the Gulf in an attempt to pressure Iran to reach an agreement over its nuclear programme.
Iranian hardline politicians have repeatedly threatened to block the strait, especially during times of heightened tensions with the United States, but it has never been closed.
Around a quarter of all seaborne oil and a fifth of the world's liquified natural gas transit through the strait, according to the International Energy Agency.
Revolutionary Guards navy commander Alireza Tangsiri said the decision to completely "close the Strait of Hormuz depends on the decision of the country's leaders".