US President Donald Trump wants Iranian ships that hinder US naval ships from being sunk.
The president says on Twitter that he has ordered the US Navy to target and destroy Iranian ships if they harass US ships.
Last week, eleven ships of the Iranian Navy approached within meters of American warships in the Persian Gulf. The US spoke of dangerous and provocative behaviour.
According to the Reuters news agency, such confrontations were frequent until a few years ago. Warning shots were also occasionally fired in 2016 and 2017.
Tensions between the US and Iran have flared up since the beginning of this year after the US killed General Qassem Soleimani in a drone attack.
America fears that Iran is working on a nuclear weapon. Iran is also said to have launched a military satellite into space this morning for the first time.