The word they are chanting is "resignation".
Public fury has erupted in Tehran piling pressure on Iran's leadership after the military admitted mistakenly shooting down a Ukrainian airliner.
All 176 on board were killed in Wednesday's (January 8) missile strike, and many were Iranians.
Relatives and friends of those who died held a vigil outside a Tehran university on Saturday (January 11).
(SOUNDBITE) (Farsi) UNIDENTIFIED FEMALE RELATIVE OF PLANE CRASH VICTIM, SAYING:
"Our children were killed in the sky. That's why we gathered together here. Where do we go?"
By the end of the day the protests had spread - riot police firing teargas at thousands on the streets in the capital and a host of other cities.
Some chanted "death to the dictator", directing their anger at Iran's top authority Ayatollah Ali Khamenei.
On Sunday (January 12), Tehran residents said police had stepped up their presence.
But the criticism is not only coming from the public: at least two moderate newspapers said those responsible for the tragedy should resign.
While criticism of the authorities is not unusual in Iran, it tends to stay in narrow boundaries.
But the press attacks and public outcry add to challenges already facing Iran's establishment, which in November saw the country's bloodiest unrest since the 1979 Islamic Revolution.
Authorities had vigorously denied responsibility for downing the plane, prior to Saturday's volte face from commanders of the elite Revolutionary Guard.
Iranian officials have sought to portray the plane disaster as a second blow to a mourning nation.
That's after the U.S. drone strike that killed top Iranian commander Qassam Soleimani, prompting an Iranian retaliation and the atmosphere of high alert in which the plane was shot down.
Soleimani's funeral had prompted huge public gatherings, which authorities described as a display of national unity.
But such emotions have been quickly overshadowed and on Saturday some protesters tore up pictures of the slain general.
As the protests spread, U.S. President Donald Trump took to Twitter - posting in English and Farsi that "we are following your protests closely, and are inspired by your courage."