The protests have been stunning in their ferocity and geographic reach, spreading to far-flung towns and cities that are strongholds of the middle and working classes.
The demonstrators themselves appeared Monday to be leaderless and their demands diffuse, ranging from better living conditions to more political freedoms and even an end to the Islamic republic. Their chants and attacks on government buildings broke taboos in a system that brooks little dissent. The demonstrations were the boldest challenge to government authority since a pro-democracy revolt in 2009.
The prospect of a harsher response from security forces, whose brutality is notorious, raised fears of further violence in a country buffeted by conflict elsewhere in the region. Iran has sent cash, weapons and fighters to prop up proxies and allies from Syria to Lebanon and Gaza — and that, too, has become a focus of the protests. The country's expensive foreign policy adventures were scorned by some demonstrators who chanted, "Leave Syria, think about us!"
At least 10 people were killed Sunday night in what state media said were clashes between police and "armed protesters" who had attempted to infiltrate security outposts. The demonstrators were from provincial areas in the south and southwestern parts of the country, including both impoverished and oil-producing regions.
One police officer was killed and three others wounded by a gunman in the city of Najafabad, about 200 miles south of Tehran, according to state media reports.
Earlier, activists said two demonstrators were shot and killed Saturday during peaceful protests.
Videos circulated online of protesters fleeing tear gas and water cannons, while others confronted police. On Monday, demonstrators again gathered in Tehran, as well as in an array of provincial cities, including Kermanshah in the west and Shiraz in central Iran, according to reports on social media. They chanted "Death to the dictator!" — referring to Supreme Leader Ali Khamenei — and called on security forces to join them.
This brought a strong rebuke from the country's judicial chief. "I demand all prosecutors across the country to get involved," said Sadegh Larijani, the Associated Press reported. Their "approach should be strong," he said.
"When it comes to regime survival, Khamenei calls the shots," Cliff Kupchan, chairman of the political risk firm Eurasia Group, said in a briefing note. "And he's got a lot of loyal and ruthless troops at his disposal."
The unrest began Thursday in the northern city of Mashhad over price increases and other economic woes. Iran's economy has been battered by years of U.S. and international sanctions, which isolated the Islamic republic for its nuclear program. Many of those sanctions were lifted as part of a nuclear deal with world powers in 2015, but few Iranians have benefited from the relief.
In contrast to the 2009 uprising — which challenged the reelection of then-President Mahmoud Ahmadinejad and was driven primarily by Tehran's educated elite — the current protests have occurred throughout the country and in traditional government strongholds.
The pro-reform figures associated with the 2009 revolt, some of whom remain under house arrest, have been noticeably absent from the political scene since the new protests began. Demonstrators have refrained from calling for the release of those figures and some of Iran's most well-known opposition leaders.
The "protesters have either become more radicalized in their demands and/or simply don't belong to the generation that experienced the events of 2009 as adults," Mohammad Ali Shabani, editor of Iran coverage at the online news portal Al-Monitor, wrote Sunday.
Iran's economy has grown since the nuclear deal thanks to resumed oil exports — Iran is a major OPEC power — but growth outside the oil sector has sagged.
Inflation is on the rise and unemployment high, at an official rate of 11.7 percent. Youth unemployment is significantly higher, at 24.4 percent, according to the government-run Statistical Center of Iran.
Young Iranians are highly educated and more modern than previous generations, and they have grown frustrated by the political and economic constraints that have kept them from achieving better lifestyles.
"There is a wide and perhaps growing disconnect with political elites," Shabani wrote.
Then, in recent weeks, proposed price increases for staples such as fuel angered many across the country.
The broad nature of the protests has perplexed Iran's leaders, some of whom have recognized the demonstrators' concerns but have called for swift action against those who break the law.
President Hassan Rouhani, a moderate who has allied with reformists, has appealed for calm, saying that demonstrators have a right to protest and criticize the government, but that they should refrain from violence. In a televised address Sunday, he acknowledged the government's lack of transparency and endemic corruption, calling on state bodies to allow more "space for criticism."
Monday, in a statement, he called the protests "an opportunity, not a threat." It was unclear whether his message would mollify the demonstrators.
Also Monday, President Trump posted on Twitter that Iran "is failing at every level" and that repressed Iranians "are hungry for food & for freedom."
"Along with human rights, the wealth of Iran is being looted," Trump continued. "TIME FOR CHANGE!"
The protests "are very unlikely to result in a revolutionary tipping point for Iran," Kupchan wrote. But they "could well recur and will inflict a hit on regime legitimacy."
"Unrest is admittedly unpredictable," he continued, adding that "coming days could take unexpected turns."