Iranian authorities have blocked popular social-media websites as protesters attempted to gather for a fourth day of antigovernment demonstrations that have already seen two deaths, in one of the most serious challenges to the leadership since the disputed presidential election of then-President Mahmud Ahmadinejad in 2009.
Users of the social-network sites Instagram and Telegram were unable to access the services on December 31, a day after two protesters died in the western town of Doroud.
Both applications are popular among Iranians and useful in helping set up gathering points for demonstrators who are disappointed with rising prices and President Hassan Rohani’s unfulfilled promises to guarantee rights to freedom of expression and assembly.
“Iranian authorities are blocking access to Telegram for the majority of Iranians after our public refusal to shut down [Sedaie Mardom] and other peacefully protesting channels,” Telegram’s Chief Executive Officer Pavel Durov said in a post on Twitter from Dubai.
Sedaie Mardom was a replacement for Amadnews, one of the largest opposition Telegram channels with more than 1.3 million followers. It was disabled after a complaint by Telecoms Minister Mohammad-Javad Azari Jahromi's on December 30.
Rohani has yet to comment on the protests. The Fars news agency said he was due to deliver a TV address to the nation later in the day, although that report has not been confirmed.
The United States has condemned the arrest of protesters, with President Donald Trump cheering on the protesters via Twitter.
Trump tweeted on December 31 that it looks like the Iranians "will not take it any longer," adding "The USA is watching very closely for human rights violations!"
Iran has dismissed Trump's tweets as "deceitful and opportunist remarks."
In the capital, Tehran, an eyewitness told RFE/RL's Radio Farda that security forces had prevented people from gathering outside Tehran University, where pro-government Basiji students are holding a gathering.
Interior Minister Abdolreza Rahmani-Fazli warned earlier on December 31 that protesters who create unrest “are responsible for their actions and should pay the price."
The semiofficial news agency Mehr quoted Habibollah Khojastepour, deputy governor of Lorestan Province, as saying on December 31 that an illegal gathering in the western town of Doroud had ignited clashes where "two of our dear Doroudi citizens were killed."
"No shots were fired by the police and security forces. We have found evidence of enemies of the revolution, Takfiri groups, and foreign agents in this clash," he added later on state television. Takfiri is a term used for Sunni militants, especially the Islamic State.
However, a video posted on social media purported to show two young men after they were shot dead by riot police.
RFE/RL could not verify the authenticity of the video, but the Voice of America (VOA) identified the victims as Hamzeh Lashni and Hossein Reshno. VOA said a reporter with its Persian Service had spoken to their families.
The video showed a protester chanting, "I will kill whoever killed my brother!"
In response, state media quoted Interior Minister Abdolreza Rahmani-Fazli as saying: "Those who damage public property, violate law and order, and create unrest are responsible for their actions and should pay the price."
The violence comes as separate state-sponsored rallies took place around the country to mark the end of the unrest that shook the country in 2009. State television reported pro-government rallies were held in some 1,200 cities and towns.
The antigovernment protests were sparked by a surge in prices of basic food supplies, such as eggs and poultry.
They quickly spread to many cities where hundreds of protesters have been chanting slogans against the Islamic establishment and the country’s supreme leader, Ayatollah Ali Khamenei.
Some have also chanted slogans against Iran’s foreign policies, including its support for the regime of Syrian President Bashar al-Assad.
Reports said that in some cities protesters set government buildings and police vehicles on fire.
Social-media videos from the city of Mashhad showed protesters overturning a police car and setting police motorcycles on fire.
The Mehr news agency posted videos of protesters attacking a town hall in central Tehran, overturning a police car, and burning the Iranian flag.
Amateur videos posted online appeared to show clashes at Tehran University, where police forces reportedly used tear gas to disperse protesters.
“Seyed Ali [Khamenei], shame on you. Leave the country alone,” protesters chanted at the university, according to a video sent to RFE/RL's Radio Farda from the Iranian capital.
In another video from Tehran, protesters appeared to tear down a Khamenei poster.
The protests took place amid reports of Internet disruptions, with the New York-based Center for Human Rights In Iran saying the government was making it difficult for Iranians to get online.
“This means that the vast majority of Iranians cannot access mobile apps or websites or anything that has its servers outside Iran without very robust circumvention tools,” the group said on Twitter.
Iran has slowed the Internet during past protests in order to prevent the spread of information, and Rahmani-Fazli warned against promoting protests online.
"We ask people not to take part in unlawful gatherings. If they plan a gathering, they should apply [for a permit], and it will be examined," he told the Young Journalists Club news website.
The hard-line Islamic Revolutionary Guards Corps and its Basij militia -- which led the crackdown against the 2009 protests -- so far has appeared to stay away from the demonstrations. However, in a statement carried by state media, it said, "The Iranian nation...will not allow the country to be hurt."
“This is more grass-roots. It’s much more spontaneous, which makes it more unpredictable,” Alex Vatanka, an Iran expert at the Middle East Institute in Washington, told The Washington Post.
“Things are not working out economically for ordinary Iranians,” he added. “But the root causes, and the much deeper resentment, go back decades. People do not feel this regime represents them.”
Dozens have been arrested during the three days of protests.
The United States condemned the arrests, with President Donald Trump warning Tehran in a tweet that "the world is watching."
"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," Trump wrote on Twitter, echoing an earlier White House statement.
"Oppressive regimes cannot endure forever, and the day will come when the Iranian people will face a choice. The world is watching!" Trump added in a tweet.
U.S. Senator John McCain later said in a tweet that “for too long, the Iranian people have been oppressed by their government, which cares more about sowing instability abroad than its own citizens.”
Iran's Foreign Ministry spokesman, Bahram Ghasemi, was quoted on state TV as saying the "Iranian people give no credit to the deceitful and opportunist remarks of U.S. officials or Mr. Trump."
With reporting by RFE/RL's Radio Farda, The Guardian, VOA, Reuters, AFP, AP, and dpa