At least two protesters have been killed in rare anti-government protests in Iran, according to a semi-official Iranian news agency.

The Mehr news agency said on Sunday that at least two people 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 behavior.

"Those who damage public property, disrupt order and break the law must be responsible for their behaviour and pay the price," Abdolrahman Rahmani Fazli said on state television early on Sunday.

Iranians began protesting on Thursday in the second 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 the 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 preplanned 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 organized weeks ago, are held every year.

'They no longer fear security forces'

Potkin Azarmehr, a blogger who focuses on the 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.

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!"

Under Trump's administration, Washington and Tehran have grown further apart, clashing on foreign policy issues such as the wars in Syria and Yemen and over the 2015 nuclear deal with world powers.

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.

PHOTO CAPTION

Anti-government rallies began as protests against high prices and have spread to several cities in Iran [Anadolu]

Al-Jazeera