CNN  — 

Iranian riot police used tear gas to disperse thousands of protesters in Tehran’s Azadi Square Sunday, as public fury escalates over Iran’s accidental shooting down of a Ukrainian passenger plane, killing all 176 people on board.

Protests that began as vigils to mourn those who died in the crash quickly turned into mass anti-government demonstrations, with calls for Supreme Leader Ayatollah Ali Khamenei to step down and for those responsible for downing the plane to be prosecuted.

“Death to the dictator,” some chanted in the capital, Tehran, in footage posted on social media. In one video, demonstrators chanted, “Khamenei have shame. Leave the country.”

Khamenei has been in office for three decades, and there is no limit to his term.

Videos circulating on social media showed demonstrators in Tehran coughing and fleeing from tear gas as authorities apparently detained protesters while others shouted for police to release them.

The Ukraine International Airlines jet that was shot down had passengers from around the world on board, but in Iran, many see the incident as a particularly domestic tragedy. Many people are angry that the government killed so many of its own people – most of those on board were Iranian nationals and people of Iranian heritage.

Some protesters could be heard shouting “we will kill whoever killed our brothers” in video posted to social media that CNN could not independently verify.

A woman attending a candlelight vigil for the victims of the Ukraine International Airlines crash, talks to a policeman following the gathering in front of the Amirkabir University in Tehran.

Image of a unified country

Protests have spread to other cities, including Shiraz, Esfahan, Hamedan and Orumiyeh, Reuters reported, exposing widespread discontent with the regime.

The angry crowds are a marked difference from the image of a unified country in mourning seen following the death of top commander Qasem Soleimani, who was killed in a US drone strike in Baghdad, Iraq last week.

Following his death, tens of thousands of people took to the streets of Tehran clutching photos of the revered and powerful figure and chanting “death to the USA.”

Widespread reverence for Soleimani, who commanded a cult-like status in the country, had seemingly united Iranians of all political stripes in anger at the US.

But at protests over the weekend, posters of Soleimani had reportedly been torn down, according to Agence France-Presse.

Security forces were deployed in key areas of the capital over the weekend, including Azadi Square near Sharif University, Enghelab (Revolution) Square near Tehran University, and Ferdowsi Square.

Fully equipped riot police were on patrol, accompanied by water cannons and black vehicles that are sometimes used as mobile detention centers.

But protesters appeared undeterred in their anger, testing the limits and patience of the Iranian regime which is known for suppressing all dissent, often brutally.

Late last year thousands of Iranians took to the streets in nationwide anti-government protests sparked by a hike in gas prices in November.