Iran's supreme leader said Tuesday that "newcomer'' President Donald Trump had shown the "real face'' of the United States, after the American leader accused Iran of being ungrateful for sanctions relief approved by the Obama administration and vowed a tougher stance.

Last week, after Iran tested a ballistic missile, Trump tweeted that the country was "playing with fire,'' saying they "don't appreciate how `kind' President (Barack) Obama was to them. Not me!''

Ayatollah Ali Khamenei, who makes the final decisions on all major policies in Iran, appeared to respond to the tweet in a remarks carried by State TV. "Why should we be thankful to the previous U.S. administration?'' he said. "Because it imposed anti-Iranian sanctions? Because of the extremist Islamic State group? Setting the region on fire in Iraq and Syria?''

He went on to mock Trump, saying: "We are thankful to Mr. Newcomer, of course, since he has shown the real face of the U.S. and proved what Iran has said for 38 years about the political, economic, social and moral corruption of the U.S. government.''

He added that the Iranian people "are not afraid of any threat.''

Trump has repeatedly criticized the 2015 nuclear agreement between Iran, the U.S. and five other world powers, in which Tehran agreed to curb its uranium enrichment in exchange for the lifting of international sanctions, but he has not said what he plans to do about it.

His administration said Iran was "on notice'' over the missile test, and imposed new sanctions on more than two dozen Iranian companies and individuals.

Iranian President Hassan Rouhani, a moderate who has worked to improve relations with the West, said earlier Tuesday that the nuclear agreement could serve as a blueprint for resolving other Middle East disputes.

As an example, he pointed to Russian-led negotiations in Kazakhstan aimed at firming up a shaky Syrian cease-fire and paving the way for the revival of peace talks to end that country's nearly six-year civil war. Iran and Russia are close allies of Syrian President Bashar Assad, while the U.S. and other Western countries support the rebels fighting to topple him. (AP)