Iran has restricted access to the Instagram and Telegram social media apps as a security measure during rare anti-government protests, according to state TV.
Irib News quoted anonymous sources as saying on Sunday that social media in the country would be temporarily limited, as the government warned protesters they would pay a price if days of unrest continued.
"With a decision by the Supreme National Security Council, activities of Telegram and Instagram are temporarily limited," the Irib News report said, without elaborating.
Facebook, which owns Instagram, did not immediately respond to a request for comment.
Pavel Durov, chief executive officer of Telegram, said on Twitter that Iran was "blocking access ... for the majority of Iranians" after protesters used the popular messaging application to plan and publicise demonstrations.
Users said on Sunday that they could no longer access the popular application via cellphone networks, though it was still available via Wifi and home internet connections.
Earlier on Sunday, Mehr, the semi-official Iranian news agency, reported that at least two protesters died on Saturday night in Dorud, a city in western Iran.
Habibollah Khojastepour, security deputy of the governor of Lorestan province, said the presence of "agitators" prevented a peaceful end to the protest, according to Mehr.
Khojastepour said neither police nor security forces fired at the protesters. He did not provide a reason for their deaths.
News of the fatalities came as Interior Minister Abdolrahman Rahmani Fazli warned demonstrators against disruptive behaviour.
"Those who abuse the police's self-restraint and composure shall be responsible to the people for the disruption and disorder," he said in a televised statement.
"Nothing will be solved by disruption and lawlessness. For us, it is well known who created this situation, provoking turmoil and promoting violence in cyberspace."
Iranians began protesting on Thursday in the second-largest city of Masshad, rallying against high prices.
The rallies have since gained momentum, spread to other cities, and are described as the largest in nearly a decade.
Saturday marked the third day of anti-government protests across Iran, when students and police clashed in Tehran.
Videos posted on Twitter by the New-York based Center for Human Rights in Iran appeared to show police in riot gear clashing with protesters outside the gates to Tehran University.
A second video showed smoke-shrouded streets, purportedly from tear gas, in the same area.
Al Jazeera could not authenticate the footage, but semi-state news agency Fars also reported confrontations between police and protesters at Tehran University.
Meanwhile, tens of thousands of people across Iran attended pre-planned pro-government rallies on Saturday to mark the end of unrest following the country's 2009 election.
State TV aired footage showing people in several cities waving flags and carrying banners bearing the image of Supreme Leader Ayatollah Ali Khamenei.
The large demonstrations, which were organised weeks ago, are held every year.
'They no longer fear security forces'
Potkin Azarmehr, a blogger who focuses on the secular pro-democracy struggle in Iran, told Al Jazeera that several groups have been protesting for some time "and now their slogans have become more radical.
"They no longer seem to have that fear from security forces," he said.
Mahan Abedin, an Iran analyst at Middle East Eye, said the protests reflect the gap between ordinary Iranians and the political elite.
The protests appeared to be "articulated by people who ostensibly have purely economic motives", he said.
"I think in keeping with longstanding culture, inevitably these protests have become political.
"[President Hassan] Rouhani has the right attitude but his government riles people. This is a very elitist government, they are bureaucratic elites, technocratic elites - they are very distant from grievances of ordinary people."
Reports said activists on social media have called for a fourth day of protests on Sunday.
Meanwhile, the US has been quick to respond to developments, warning Tehran against arresting peaceful protesters.
US President Donald Trump has posted a series of tweets on Iran, most recently writing: "Oppressive regimes cannot endure forever. The world is watching!"
In response to Trump, Bahram Qassemi, spokesman for Iran's foreign ministry, called the US president's warnings "cheap, worthless and invalid", according to the semi-state news agency Fars.
"Iranian people feel no value for the opportunistic claims of the US officials and Mr. Trump, himself," Qassemi was quoted as saying.