Iran has launched several ballistic missiles from silos across the country as part of a military exercise, state media say, defying US pressure.
The Revolutionary Guards said in a statement that the tests demonstrated the country's "deterrent power".
US officials said that if the reports were confirmed, they would raise the matter at the UN Security Council.
In January, the US imposed sanctions targeting Iran's missile programme in response to the last round of tests.
UN experts said those tests had violated a Security Council resolution.
Resolution 1929, which barred Iran from undertaking any work on "ballistic missiles capable of delivering nuclear warheads", was terminated after a nuclear deal between Iran and six world powers was implemented two months ago.
A new resolution, 2231, then came into force that "calls upon" Iran not to undertake any activity related to "ballistic missiles designed to be capable of delivering nuclear weapons".
Iran says it does not have nuclear weapons and will continue missile development.
Iranian state television reported on Tuesday that the missiles were fired from silos at various locations, without naming them.
It broadcast pictures of one of the night-time launches, and a presenter said the missile was a medium-range Qiam-1, according to the Reuters news agency.
The Revolutionary Guards' statement said the tests were intended "to show Iran's deterrent power and also the Islamic Republic's ability to confront any threat against the [Islamic] Revolution, the state and the sovereignty of the country".
The head of the Guards' Aerospace Force, Brig Gen Amir Ali Hajizadeh told state television that the missiles had "struck a target 700km (435 miles) away".
He warned the US was "trying to turn off the lights of Iran's missile programme", adding: "The Guards don't give into threats."
US state department deputy spokesman Mark Toner said it was "aware of and following closely" the reports of the missile tests.
"If confirmed, we intend to raise the matter in the UN Security Council. We will also encourage a serious review of the incident and press for an appropriate response."
"This development underscores why we continue to work closely with partners around the world to slow and degrade Iran's missile programme."
Mr Toner also said the US would "continue to aggressively apply our unilateral tools to counter threats from Iran's missile programme".
While any missile of a certain size could in theory be used to carry a nuclear warhead, Iran says its missiles are for use solely as a conventional deterrent.
It claims to have ballistic missiles with a range of 2,000km (1,250 miles) that would be capable of reaching Israel and US military bases in the Middle East.