Naval forces of Iran's Revolutionary Guards have seized a ship "carrying smuggled fuel" in the Gulf and arrested four crew members, local media reported.

"More than 50,000 litres of smuggled fuel were discovered" on board the ship, Fars News Agency quoted the chief justice of the coastal Hormozgan province, Mojtaba Ghahramani, as saying on Saturday.

He said the Islamic Revolutionary Guard Corps (IRGC) navy had "confiscated" the ship and "arrested four people" during the operation.

Neither the origin of the ship nor the date of the operation were immediately disclosed.

Ghahramani said the fuel would be redirected to the country's "legal distribution network".

The United States military has, in recent weeks, beefed up its presence in the Gulf after accusing Iran of seizing or attempting to take ships in the vital waterway.

On July 6, the US Navy said the IRGC seized a commercial vessel in the Gulf, a day after it accused Iranian forces of two similar attempts off the coast of Oman.

Iran later said the vessel seized in the Gulf was carrying "more than one million litres of smuggled fuel".