President Donald Trump has warned Iran's Supreme Leader, Ayatollah Ali Khamenei, to be "very careful with his words" after the Iranian called the U.S. leader a “clown” during a rare sermon he delivered earlier on Friday.

"The so-called 'Supreme Leader' of Iran, who has not been so Supreme lately, had some nasty things to say about the United States and Europe," Trump tweeted on January 17.

"Their economy is crashing, and their people are suffering. He should be very careful with his words!" Trump tweeted.

Trump also tweeted that “the noble people of Iran—who love America—deserve a government that's more interested in helping them achieve their dreams than killing them for demanding respect. Instead of leading Iran toward ruin, its leaders should abandon terror and Make Iran Great Again!”

Following the killing of Iran's top general in Iraq by a U.S. drone attack on January 3 and the downing of a Ukrainian airliner by Iran's Revolutionary Guard January 8 followed by protests, the embattled Khamenei decided to deliver his first sermon in eight years.

During the much-anticipated event, Iran's top ruler mostly repeated his hardliner positions regarding the United States and he also lashed out at Western European nations who are signatories of the 2015 nuclear agreement for adopting a tougher stance toward Iran.

Khamenei also reiterated his commitment to maintain a military presence in the region, by saying that the Revolutionary Guard have no boundaries.