US President Donald Trump has warned Iran that the "world is watching" after two days of anti-government protests sparked by the country's economic woes.
Hundreds of people took to the streets in Mashhad, Iran's second-largest city and one of the holiest places in Shia Islam, on Thursday.
The protests spread to Tehran and other cities on Friday, with police using water cannons in some cases to disperse the crowds.
Initially aimed against high prices, the anti-government protests quickly turned against the Islamic regime as a whole.
Police arrested 52 people. On Saturday, tens of thousands of government supporters marched in cities across Iran in a show of strength for the regime.
Many of the marchers carried banners in support of Supreme Leader Ayatollah Ali Khamenei.
But local media reported that small anti-government protests were continuing around the University of Tehran.
Many reports of peaceful protests by Iranian citizens fed up with regime’s corruption & its squandering of the nation’s wealth to fund terrorism abroad. Iranian govt should respect their people’s rights, including right to express themselves. The world is watching! #IranProtests
— Donald J. Trump (@realDonaldTrump) December 30, 2017
Mr Trump tweeted in support of the anti-government protests.
"Many reports of peaceful protests by Iranian citizens fed up with regime's corruption and its squandering of the nation's wealth to fund terrorism abroad," he wrote.
"Iranian govt should respect their people's rights, including right to express themselves. The world is watching!"
And the US State Department condemned the arrest of peaceful protesters and urged "all nations to publicly support the Iranian people and their demands for basic rights and an end to corruption".
An Iran's Foreign Ministry spokesman, Bahram Ghasemi, dismissed the comments coming from Washington, saying that "Iranian people give no credit to the deceitful and opportunist remarks of US officials or Mr Trump."
The US President has refused to re-certify a 2015 deal between Tehran and world powers that curbed Iran's disputed nuclear programme in return for a lifting of most international sanctions.
The deal was one of the biggest achievements by President Hassan Rouhani, but has yet to bring the broad economic benefits.
State television said pro-government rallies were scheduled to be held in more than 1,200 cities and towns on Saturday.
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The government-sanctioned rallies have been held annually to mark the end of protests surrounding Iran's disputed 2009 presidential election.
Protesters at the time said the vote, which marked Mahmoud Ahmadinejad's re-election as president, was rigged, and tens of thousands of people staged street protests for eight months.