From the VOA:

Witnesses in Iran’s capital Tehran say riot police used tear gas on Saturday in an effort to disperse thousands of protesters.
State television said police clashed with what it called “rioters.” Iran has greatly restricted international media coverage in the country, but witnesses speaking to VOA’s Persian News Network and other news agencies say thousands of residents were in the streets attempting to stage protests in defiance of warnings by the government.
There was a heavy police presence at Enghelab Square, where the opposition had called for the latest protest.