Iranian Supreme Leader Ayatollah Ali Khamenei says US President Donald Trump has shown “the real face of America”.
In his first speech since Mr Trump took office, Mr Khamenei said the president had exposed “political, economic, moral and social corruption” in the US.
The response follows Mr Trump’s imposition of new sanctions on Iran over a ballistic missile test.
Mr Trump has also been a fierce critic of the landmark nuclear deal struck between Iran and world powers in 2015.
Mr Khamenei, addressing military commanders in the capital Tehran, said Mr Trump was trying to frighten Iranians, but would fail.
“We are thankful for this person who has arrived [President Trump]. Our thanks is for making our life easy as he showed the real face of America,” he said.
“What we have been saying for more than 30 years about the political, economic, moral and social corruption in the US ruling system, this person arose during the election campaign and… has confirmed it.”
Mr Khamenei called on Iranians to turn out in large numbers on Saturday to mark the anniversary of the 1979 Islamic revolution.
His speech comes amid an escalating war of words between Iran and the US.
US Defence Secretary James Mattis recently called Iran the world’s “biggest state sponsor of terrorism”.
Iran confirmed last week it had tested a missile but denied violating a UN Security Council resolution on its nuclear activities.
A US statement said Iran’s “continued support for terrorism and development of its ballistic missile programme poses a threat to the region”.
In a tweet, President Trump accused Iran of playing with fire, adding: “They don’t appreciate how ‘kind’ President Obama was to them. Not me.”
Iranian Foreign Minister Mohammad Javad Zarif said on Tuesday he believed that Mr Trump would try to renegotiate the nuclear deal but that “Iran and European countries will not accept that”.
“We will have difficult days ahead,” he told the Ettelaat newspaper.
Under the deal, Iran agreed to curb its sensitive nuclear activities in return for the lifting of economic sanctions.