In 2009, protesters were supporting reformers, but now their discontent appears to be with their leaders in general.
In an unusually bold act of defiance, some protesters in Tehran and elsewhere called for the resignation of Iran’s supreme leader, Ayatollah Ali Khamenei, and witnesses described crowds chanting, “Death to the dictator” and “Clerics should get lost.”
Video shared on social media showed the police in Tehran firing water cannons to try to disperse demonstrators in Ferdowsi Square, Reuters reported, although the footage could not be independently confirmed.
Two protesters were reported killed in recent days in the city of Dorud, and there were reports of dozens arrested across Iran.
With the Iranian news media tightly controlled, it remained difficult to assess the extent of the protests. But they were clearly severe enough that Mr. Rouhani felt the need to respond.
State television also said the authorities would temporarily restrict access to Instagram and the messaging app Telegram, to “maintain peace.” Reports about the demonstrations were being spread on such platforms.
The protests flared against the backdrop of a deep economic malaise in Iran, punctuated by rising prices and high unemployment, especially among young people.
Mr. Rouhani decisively won re-election in May, partly on Iranian hopes that his successful negotiation of a landmark nuclear agreement in 2015 with big foreign powers, including the United States, would lead to an economic renaissance and greater prosperity in the nation of 80 million.
Those hopes, however, have so far turned into disappointment. Despite the relaxation of nuclear-related economic sanctions and increased sales of oil — Iran’s most important export — core American restrictions including a ban on Iranian use of the United States banking system remain in place, severely limiting Iran’s efforts to become less isolated economically.
While a few big name multinational corporations like France’s Total and Renault have engaged with Iran since the nuclear deal took effect, many foreign companies are reluctant to make big commitments in the country. And President Trump’s threats to scrap the nuclear agreement have given potential investors in Iran more reason to hesitate.
Mr. Rouhani’s failure to improve people’s livelihoods has been further aggravated by recent price spikes in staples like eggs, coupled with the government’s plans to sharply reduce subsidies that many Iranians are accustomed to receiving. So resentment toward the government over economic issues is not unexpected.
While the Iranian authorities appear to have been surprised by the spontaneity and speed of the demonstrations, outside analysts have little doubt that Mr. Khamenei and his subordinates would use force to suppress them if they felt it necessary. And there is little to suggest that the protesters have leaders or a cohesive message, like those in the 2009 uprising.
“The ongoing protests, by contrast, show no well-defined demands, no leadership or organization, and are diffuse around Iran,” Cliff Kupchan, the chairman of the Eurasia Group, a Washington-based political risk consultancy, said in an advisory emailed to clients on Sunday. But he also cautioned: “unrest is admittedly unpredictable — coming days could take unexpected turns. Signposts of a surprise include; a leader or small group of leaders emerging, a defined manifesto, and much larger protests.”
President Trump doubled down on his frequent criticism of the Iranian government on Sunday. He posted on Twitter: “The people are finally getting wise as to how their money and wealth is being stolen and squandered on terrorism. Looks like they will not take it any longer. The USA is watching very closely for human rights violations!”
In an apparent response to Mr. Trump on Sunday, Mr. Rouhani said: “This man who today in America wants to sympathize with our people has forgotten that a few months ago he called the Iranian nation terrorist,” according to PressTV. “This person who is against the Iranian nation from head to toe has no right to feel sorry for the people of Iran.”
Senator Lindsey Graham, Republican of South Carolina, said he had talked to President Trump on the phone on Sunday morning to urge him to be more forceful with the Iranian government. “It’s not enough to watch,” Mr. Graham said on CBS’s “Face the Nation.” “President Trump is tweeting very sympathetically to the Iranian people. But you just can’t tweet here. You have to lay out a plan.”
Mr. Trump later tweeted about Iran’s blocking of some social media, saying it was keeping peaceful demonstrators from communicating. He added, “Not good!”
On Sunday, Telegram’s chief executive, Pavel Durov, confirmed that the app had been blocked, posting a statement on Twitter that said, “Iranian authorities started blocking Telegram in Iran today after we publicly refused to shut down channels of peaceful Iranian protesters.”
He added: “We are proud that Telegram is used by thousands of massive opposition channels all over the world. We consider freedom of speech an undeniable human right, and would rather get blocked in a country by its authorities than limit peaceful expression of alternative opinions.”