Tens of thousands gathered in cities across Iran on Wednesday in a massive show of support for the regime after days of deadly unrest, state television showed.
Crowds chanted "Leader, we are ready" as images showed vast numbers marching through the cities of Ahvaz, Kermanshah, Gorgan and elsewhere.
The crowds waved Iranian flags and pictures of supreme leader Ayatollah Ali Khamenei, as well as placards reading "Death to seditionists".
"We offer the blood in our veins to our leader," was another popular chant.
The rallies followed several days of unrest - initially sparked by protests over economic problems but quickly turning against the regime as a whole - in which 21 people lost their lives and hundreds were arrested.
The rallies come after Khamenei on Tuesday blamed days of protests across the country on meddling by "enemies of Iran."
The US has branded as "complete nonsense" Iran's accusation that its enemies have been behind a wave of violent protests sweeping the country.
Nikki Haley, US envoy to the UN, said the protests were "spontaneous", adding that the US planned to call an emergency UN meeting on the situation.
While President Hassan Rouhani initially offered conciliatory words, saying the protesters had legitimate grievances over the state of the economy, the government’s stance has hardened in recent days.
The head of Tehran’s Revolutionary Court warned that protesters could face the death penalty if convicted of moharebeh, waging war against God, while state television said those arrested after the first 48 hours of demonstrations would be treated more severely.
Around 1,000 people have been arrested so far, authorities said.