At the center of the protests is discontent with Iran's free-falling currency. The rial has lost as much as 80% of its value against the U.S. dollar in the last year, and its plunge has accelerated at a record pace in recent days.
Mark Dubowitz, a sanctions expert at the Foundation for Defense of Democracies, said the rial's fall may be a sign that Iran doesn't have the foreign exchange reserves needed to prop up the currency, or at least can't access reserves that might be in accounts abroad that have been frozen by sanctions.
"You'd think that if the regime had sufficient reserves, and access to them, they could be intervening to prevent the rial from plummeting further," he said.
The poor and middle classes have been hit especially hard as prices for food and other necessities have soared.
At the Istanbul intersection, protesters arrived as police were raiding the shops and corner hangouts of many money-changers. The operation was part of a crackdown on illegal sales of U.S. dollars, which are growing in popularity as a hedge against the dwindling value of the rial. Authorities blame these transactions in part for the rial's declining value.