Thousands of pro-government demonstrators are attending rallies in Iran, after two days of anti-government protests.
State TV showed crowds of black-clad supporters in the capital, Tehran.
Dozens of people have been arrested during days of protests over corruption and living standards, which the vice-president suggested were being organised by political opponents.
The US administration warned Iran that “the world was watching” its response.
Saturday’s official rallies were organised in advance of the anti-government protests, to mark the eighth anniversary of the suppression of major street protests.
In 2009, masses came out in favour of the then-president, Mahmoud Ahmadinejad, in response to protests by reformists over a disputed election which returned him to power.
Meanwhile, the Iranian authorities are blaming anti-revolutionaries and agents of foreign powers for the protests.
‘A show of force’
The authorities hope the government-sponsored demonstrations throughout the country will be a show of force. The state-run television – a bastion of the Islamic hardliners in Iran – is reporting a massive turnout, focusing on the demonstrators’ support for the supreme leader, Ayatollah Ali Khamenei.
He has been the focus of much anger in the anti-government demonstrations of the past two days, with protesters calling on him and the clerical regime to go.
The protests have been the biggest expression of discontent in the country for several years. On social media, there are calls for more action later on Saturday in a number of towns and cities.
But signs are that the police may want to deal with any break out of fresh protests with force, although the authorities admit there is widespread discontent in the country, and not just about rising prices.
How did the anti-government demonstrations start?
People there took to the streets to express anger at the government over high prices, and vented their fury against President Hassan Rouhani. Fifty-two people were arrested there for chanting “harsh slogans”.
The protests spread to at least half a dozen cities on Friday. In some cities police in riot gear and on motorbikes clashed with demonstrators.
Some protests developed into broader demonstrations against the authorities, calling for the release of political prisoners and an end to police beatings. It was the biggest display of public dissent since huge pro-reform rallies in 2009.
Overall, the numbers said to be taking part range from less than 100 in some places to thousands in others – but demonstrations do not appear to be taking place on a massive scale.
Some reports suggest that calls for further protests on Saturday have already been heeded.
— سامی (@Sami8094) December 30, 2017
What is Iran saying about the protests?
First Vice-President Eshaq Jahangiri has suggested that government opponents are behind the protests, according to comments reported by state broadcaster IRIB.
He said: “Some incidents in the country these days are on the pretext of economic problems, but it seems there is something else behind them. They think by doing this they harm the government, but it will be others who ride the wave.”
The governor-general of Tehran said that any such gatherings would be firmly dealt with by the police, who are out in force on the main roads.
Officials in Mashhad said the protest was organised by “counter-revolutionary elements”, and video online showed police using water cannon.
What was the US response?
“The Iranian government should respect their people’s rights, including their right to express themselves. The world is watching,” White House spokeswoman Sarah Huckabee Sanders said on Twitter.
The same tweet later appeared on President Donald Trump’s Twitter account.
The US State Department urged all nations “to publicly support the Iranian people and their demands for basic rights and an end to corruption”.
U.S. strongly condemns arrest of peaceful protestors in #Iran, urges all nations to publicly support Iranian people. As @POTUS said, longest-suffering victims of Iran's leaders are Iran's own people. #Iranprotests pic.twitter.com/mUTObTeHft
— Heather Nauert (@statedeptspox) December 29, 2017
What is behind the unrest?
The protests were initially against economic conditions and corruption but appear to have turned political.
Slogans have been chanted against not just Mr Rouhani but Supreme Leader Ayatollah Ali Khamenei, and clerical rule in general.
Demonstrators were reportedly heard yelling slogans like “The people are begging, the clerics act like God”. Protests have even been held in Qom, a holy city home to powerful clerics.
There is also anger at Iran’s interventions abroad. In Mashhad, some chanted “not Gaza, not Lebanon, my life for Iran”, a reference to what protesters say is the administration’s focus on foreign rather than domestic issues.
Other demonstrators chanted “leave Syria, think about us” in videos posted online. Iran is a key provider of military support to the government of Bashar al-Assad in Syria.
It is also accused of providing arms to Houthi rebels fighting a Saudi-led coalition in Yemen, which it denies, and is an ally of Lebanon’s powerful Shia movement Hezbollah.