Saturday's show of support took place a day after Iran's foreign minister said a United Nations Security Council meeting called by the United States to discuss the protests had proved a "blunder" by the administration of U.S. President Donald Trump.
State television showed rallies and marches in more than a dozen cities with demonstrators waving Iranian flags and chanting slogans including "Death to America", "Death to Israel" and "Death to Britain".
More than a week of unrest has seen 22 people die and more than 1,000 arrested, according to Iranian officials, in the biggest anti-government protests for nearly a decade.
Unrest spread to more than 80 cities and rural towns as thousands of young and working-class Iranians voiced anger at graft, unemployment and a deepening gap between rich and poor.
Residents contacted by Reuters in various cities have said the protests had subsided in recent days, after the government intensified a crackdown by dispatching Revolutionary Guards forces to several provinces.
On Saturday, videos on social media showed a heavy police presence in cities, including Khorramabad in southwestern Iran where on Wednesday evening social media posts showed protesters throwing stones at riot police.
The protests have drawn largely young people and workers as well as members of the educated middle-class that formed the backbone of a pro-reform revolt almost a decade ago.
The provincial governor in northeastern Mashhad, where the protests started, was quoted as saying on Saturday that 85 percent of detainees there had been released after signing a pledge not to re-offend.
"Those with a criminal record, or those charged with sabotage such as setting fire to motorcycles or damaging public buildings have been referred to judicial authorities," governor Alireza Rashidian told the ISNA news agency.
A police spokesman said most of those arrested were "duped" into joining the unrest and had been freed on bail, the state news agency IRNA reported. "But, the leaders of the unrest are held by the judiciary in prison."
Tehran University Vice-President Majid Sarsangi said the university had set up a committee to track the fate of students arrested during the unrest.
"Our efforts at the university are aimed at cooperating with the relevant authorities to create the conditions for the return of the detained students to the university and their families in the shortest possible time," Sarsangi told ISNA.
Separately, a member of parliament said about 90 students were detained, 10 of whom were still not accounted for.
"It seems that the total number of detainees is around 90. Ten students from universities in Tehran and some other cities are in an uncertain position, and ... it is still unknown which body has detained them," the labor news agency ILNA quoted reformist politician Mahmoud Sadeghi as saying.
Iran has several parallel security bodies and residents say arrests are often not immediately announced.
Videos that appeared on social media in recent days showed relatives of detainees gathering outside prisons seeking information about the fate of their loved ones.
In Europe, hundreds of Iranians held rallies on Saturday in support of the anti-government protests in Iran, in cities including Stockholm, London, Paris and Berlin.
About 400 people gathered in central Paris, and several hundred held a rally in front of Berlin's Brandenburg Gate with Iranian flags, drums and banners calling for a change of government.
One of the protesters in Berlin, 18-year-old Pariya Kohandel Saleh, said her father was in jail in Iran for supporting the families of prisoners.
"Things should be good in Iran now the sanctions have been lifted, but the mullahs' pockets are bottomless and everybody knows it," she told Reuters.
A United Nations Security Council meeting on Friday to discuss the protests turned into criticism of the United States for requesting to meet on what some member states said was an internal issue for Iran.
Foreign Minister Mohammad Javad Zarif tweeted: "The UNSC rebuffed the U.S.'s naked attempt to hijack its mandate ... Another FP (foreign policy) blunder for the Trump administration."
Iran's elite Guards and its affiliated Basij militia suppressed unrest in 2009 over alleged election fraud, in which dozens of pro-reform Iranians were killed.
(For graphic on Iranian protests, click http://tmsnrt.rs/2CXDYXZ)
(Reporting by Dubai newsroom, additional reporting by Michelle Martin in Berlin; Editing by Ros Russell)