(CNN) Iran's Supreme Leader, Mojtaba Khamenei, said on Saturday that US President Donald Trump's signature is "worthless and cannot be relied upon" after "repeated violations of the memorandum of understanding" between the United States and Iran.

Khamenei's remarks came in a written statement published by official media. The Supreme Leader has not appeared publicly since the beginning of the war.

In the statement, Khamenei criticized the United States for launching military strikes at a time when Iran was holding the funeral of his father, former Supreme Leader Ali Khamenei.

The Iranian leader said: "At a time when this great public display was taking place, the repeated violations of the memorandum of understanding signed between the presidents of Iran and the United States by the 'Great Satan' have once again demonstrated to everyone how worthless and unreliable the US president's signature is. Bullying, ambition for hegemony, and brutality are inseparable elements of the American approach."

Khamenei added that Iran will teach the United States "unforgettable lessons" for its attempts to "fuel war and inflict heavy losses."

He said: "The courage of the fighters of Islam and the bravery of the people of southern Iran in recent days have demonstrated examples of these lessons."

He also addressed the Iranian people, urging them to continue trusting government officials, saying: "The enemy must not see any sign of weakness from our side."