Iran’s leaders are facing growing calls to dismiss senior officials after a Ukrainian passenger plane was shot down killing all 176 people on board.
Thousands of protesters demanded accountability on Saturday after the military said it had mistakenly downed the jet, having earlier denied it.
Riot police have been deployed and there are reports that protesters have gathered for a second day of action.
The plane was shot down amid rising tensions with the US.
It happened shortly after Iran launched missiles at two airbases housing US forces in Iraq. Those strikes were a response to the US killing of senior Iranian commander Qasem Soleimani in a drone strike in Baghdad on 3 January.
Dozens of Iranians and Canadians, as well as nationals from Ukraine, the UK, Afghanistan and Sweden died on the plane.
It was en route to the Ukrainian capital, Kyiv, but came down near Imam Khomeini Airport in Tehran shortly after take-off.