Pro-government rallies in several Iranian cities have drawn thousands of marchers.
It follows six days of rarely-seen unrest that have caught the country's leaders off-guard.
State television has broadcast live footage of rallies in Kermansheh, Ilam and Gorgan. Marchers waved Iranian flags and pictures of Supreme Leader Ayatollah Ali Khamenei.
Marchers are voicing their support for Khamenei, chanting "The blood in our veins is a gift to our leader" and "We will not leave our leader alone".
"The seditionist rioters should be executed," others chanted. Some carried posters claiming hostile "hidden hands" guided from the United States, Israel and the United Kingdom should be cut off.
What is this in response to?
What analysts are describing as the boldest challenge to Iran's established order in almost a decade.
Demonstrations continued into Tuesday night with postings and video footage on social media showing riot police deployed in force in several cities.
Have the earlier protests been violent?
Yes. At least 21 people have been killed during the unrest, including two members of the security forces.
More than 450 protesters have been arrested in the capital Tehran in recent days. Officials say hundreds of others have been detained around the country.
Judicial officials say come could face the death penalty.
What has the government said?
Khamenei has accused Iran's foes of fomenting the unrest.
In an attempt to control the flow of information and calls for anti-government gatherings, the authorities in Tehran have restricted access to the Telegram messaging app and Instagram.
The protests, which began over economic hardships, have taken on a rare political dimension. A growing number of young people are reportedly calling on Khamenei to step down.
They are the biggest since unrest in 2009 that followed the disputed re-election of the then-President Mahmoud Ahmedinejad.
High prices, alleged corruption and mismanagement are fuelling the anger. Youth unemployment topped 28.8% last year.
President Hassan Rouhani championed a deal struck with world powers in 2015 to curb Iran's nuclear programme in return for the lifting of international sanctions.
However, he has failed to deliver on promises of prosperity in the OPEC oil producer.
The nuclear deal is facing its biggest challenge since it was struck. US President Donald Trump due to decide by mid-January whether to continue waiving US sanctions or re-impose them.