Iran says it has tested a new medium-range missile during war games near a vital Gulf oil transit channel.
The announcement comes hours after US President Barack Obama signed a law tightening sanctions against Tehran over its nuclear programme.
A military spokesman also announced that Iranian ships and submarines will tomorrow carry out manoeuvres designed to allow them to shut the Strait of Hormuz if Tehran so wishes.
The show of military muscle underlined a threat by Iran to shut the narrow strait - a strategic channel and through point for 20% of the world's oil - if more Western sanctions were applied over its nuclear programme.
The potential for that scenario, and possible confrontation with US warships that patrol the Gulf, was given impetus when Mr Obama yesterday signed tough new sanctions targeting Iran's central bank and financial sector.
Under the measures, foreign firms will have to choose between doing business with the Islamic republic or the United States.
The aim is to put the squeeze on Iran's crucial oil revenues, most of which are processed by the central bank.
The new US sanctions were "unjustifiable," Mohammad Nahavandian, the head of Iran's chamber of commerce, told the ISNA news agency.
He said previous sanctions had "failed to halt Iran's trade."
Iran has said new sanctions, including a possible oil embargo being mulled by the European Union, could push it to close the Strait of Hormuz.
"From tomorrow morning (Monday), a vast majority of our naval units - surface and underwater, and aerial - will implement a new tactical formation, designed to make the passage of any vessel through the Strait of Hormuz impossible if the Islamic Republic of Iran's navy so chooses," navy spokesman Commodore Mahmoud Mousavi was quoted as saying by the ISNA news agency.
Today "for the first time, an anti-radar medium-range missile was successfully fired during the massive naval drills," Mr Mousavi said, according to state media.
"This medium-range surface-to-air missile is equipped with the latest technology to combat radar-evading targets and intelligent systems which try to disrupt missile navigation," he was quoted as saying.
The missile was fired from a warship, the Fars news agency said.
Other details about the weapon were not immediately known, notably what distance it is able to fly.
