TEHRAN — Iran was plunged into a nationwide internet blackout Thursday evening as anti-government protests spread around the country.

Footage verified by CNN showed mass protests in cities across Iran, with demonstrators blocking roads and setting fires in the streets of the capital.

In the videos, opposing factions demonstrating across the country rallied around chants in support of and opposition to the Iranian government.

Iranian state media downplayed the scale of Thursday's unrest. In some cases, they denied protests had taken place altogether, posting videos of empty streets.

The peaceful demonstrations in Tehran and the second city of Mashhad on Thursday evening, which were not dispersed by security forces, can be seen in footage verified by BBC Persian.

Thousands of people took to the streets across the capital, starting at about 8 pm local time (16:30 GMT) on Thursday, Al Jazeera reporter Tohid Asadi said from Tehran early Friday.

“What we saw was many more neighborhoods in the Iranian capital coming to the streets. Several streets were blocked while I was driving from downtown,” Asadi said, noting that confrontations took place between protesters and police.

What began as organized protests in Tehran’s bazaars and universities has morphed into thousands marching through the streets in a movement that has increased pressure on the ruling regime. Protests turned violent after the deployment of government security forces.

At least 21 people, including security forces, have been killed since the demonstrations began, according to a tally by the AFP news agency, citing local media and official statements.

The US-based Human Rights Activist News Agency (HRANA) has said at least 34 protesters — five of them children — and eight security personnel have been killed, and that 2,270 other protesters have been arrested.

Norway-based monitor Iran Human Rights (IHR) has said at least 45 protesters, including eight children, have been killed by security forces.

The Fars News Agency said 950 police officers and 60 personnel from the paramilitary Basij force have been injured in the protests.

Iranian news outlets reported Thursday that at least five security personnel have also been killed in the unrest, including two members of Iran’s Islamic Revolutionary Guard Corps.

The numbers could not be independently verified, and Iranian state news organizations have sometimes reported individual deaths without providing a comprehensive tally.

Authorities cut internet access and telephone lines immediately after Thursday’s protests in the capital Tehran and other major cities began, although the blackout did not immediately prevent the posting of videos of the protests, now well into their second week.

“National blackouts tend to be the regime’s go-to strategy when deadly force is about to get used against protesters,” Alp Toker, director of cybersecurity watchdog NetBlocks, told CNN, “with the goal being to prevent the spread of news of what’s happening on ground, and also to limit international scrutiny.”

From as far west as Ilam, a Kurdish-majority region bordering Iraq, to Tehran and Mashhad, in the northeast near the Afghan border, people in more than 100 cities have taken to the streets since protests first erupted 12 days ago.

Protesters can be heard in the footage calling for the overthrow of Iran's Supreme Leader Ayatollah Ali Khamenei and the return of Reza Pahlavi, the exiled son of the late former shah, who had urged his supporters to take to the streets.

At least some protesters appeared to be heeding the call by Pahlavi, whose father was overthrown by the 1979 Islamic revolution and lives in Washington, to turn out Thursday. One of the slogans shouted by the marchers was “This is the last battle, Pahlavi will return,” according to video reviewed by CNN.

Pahlavi thanked US President Donald Trump for holding the "regime to account", and called on European leaders to do the same.

The unrest prompted Trump on Thursday to repeat his threat to attack Iran if security forces kill protesters.

“I have let them know that if they start killing people, which they tend to do during their riots … we’re going to hit them very hard,” Trump told radio host Hugh Hewitt.

Iranian journalist and activist Masih Alinejad told CNN’s Jake Tapper on Thursday that the protests had expanded beyond economic matters.

“This is very clear that they’re saying that this regime can no longer be reformed. So they’re saying we want an end to the Islamic Republic,” Alinejad said.

Exacerbating the situation, the central bank decided last week to end a program allowing some importers to access cheaper US dollars compared to the rest of the market — a decision that led shopkeepers to increase prices.

Prices of basic goods like cooking oil and chicken dramatically spiked overnight, and some products vanished all together. The volatility pushed the bazaaris to close shop, a drastic measure for a group traditionally supportive of the Islamic Republic.

After days of protests and crackdowns, the reformist-ruled government attempted to alleviate the pressure by offering direct cash handouts of almost $7 per month, although it said at the same time that this measure alone could not solve the crisis.

“We should not expect the government to handle all of this alone,” President Masoud Pezeshkian said in a televised speech Monday.

Experts said the leaderless and uncoordinated movement turned violent as economic protests intertwined with political ones.

Iranian provinces Ilam and Lorestan, have emerged as hot spots. Fueled by ethnic division and poverty, crowds set fires in the streets and chanted “Death to Khamenei,” directly challenging Iran’s supreme leader, Ayatollah Ali Khamenei, who holds ultimate authority over the nation’s religious and state affairs.

Video geolocated by CNN to a public square in Mazandaran provice in Iran’s far north shows a large crowd of protesters calling for the removal of Khamenei.

“This is the year of blood,” they chant, “Seyyed Ali (Khamenei) is going to fall.”

In Mashhad — Iran’s second-largest city and Khamenei’s hometown — demonstrators can be seen lowered and tearing apart an Iranian flag, in video distributed by Reuters.

And in footage released by IranWire from the northwest city of Tabriz, shots could be heard in the background as protesters walked on a roadway. It was unclear whether the shots were from authorities using live rounds.

The Iran Human Rights NGO (HIRNGO) said, “State forces have used live ammunition to suppress the protests and have carried out widespread, mass arrests in some cities.”

President Pezeshkian earlier called on security forces to exercise "utmost restraint" when handling peaceful protests. "Any violent or coercive behaviour should be avoided," a statement said. — Agencies