Demonstrations against Israel's military action in Gaza and in support of Palestinians took place in Tehran and 700 other Iranian cities after Friday Muslim prayers, news agency ISNA said.
Protesters chanted "death to America" and "death to Israel" in the capital, in demonstrations called for by the authorities.
"One must salute the Palestinians' popular resistance and the response they have given to the Zionist regime (by firing rockets into Israel)," Ayatollah Ahmad Khatami said at the weekly prayers in Tehran, IRNA news agency said.
"Your method is good and you can bring the Zionist regime to its knees," he added.
Iran urged the United Nations and European Union on Thursday to stop Israel's "barbaric" offensive against armed Palestinian groups in Gaza, calling the operation "organised terrorism."
"Immediate and serious action by international (organisations) is needed to end the military campaign against the people of Gaza," Foreign Minister Ali Akbar Salehi said in a statement.
Iran does not recognise arch-enemy Israel, and supports Palestinian movements such as Hamas in the face of what it calls the illegal occupation of the Palestinian territories.