Iran police clash with protesters over currency crisis
Tear gas was used to disperse the demonstrators, some of whom were setting fire to tyres and rubbish bins. There were many arrests, reports say.
Eyewitnesses told the BBC that scores of people gathered outside the central bank, calling for the governor to stand down, chanting anti-government slogans.
The rial has plummeted to record lows against the US dollar in recent days.
Eyewitnesses told BBC Persian that riot police fired tear gas to disperse the crowds.
Reports say many shops in the central Grand Bazaar brought down their shutters in sympathy with the demonstrators.
Traders are angry at the lack of direction from the government in the crisis, which they say has led to more instability in prices and made trading almost impossible, according to commentators.
Viewers of BBC Persian television in Iran reported that authorities began jamming the channel's signals on two satellites after the London-based Persian-language channel reported the Tehran protests.
President Ahmadinejad has blamed Western sanctions for the fall in the rial, saying they amounted to an economic war.
However, many Iranians accuse him of financial mismanagement.
Iranian media reaction
The conservative daily, Khorasan, asked: "Mr Ahmadinejad, are you the country's president?" It said the president had failed at a news conference on Tuesday to say "what 'programmes' and 'new plans' the government has to resolve the situation".
The reformist newspaper, Etemad, carried an editorial headlined "Why can't you?" saying that "once again Ahmadinejad took no responsibility for the chaotic situation".
The conservative news website, Baztab-e Emruz, pointed to the negative impact of the president's remarks on the decline in the rial's exchange rate. "An hour after Ahmadinejad's news conference... the rate of the dollar, which had reduced to 3,200 tomans [32,000 rials approx] in the afternoon, increased to 3,550 again," it said.
The moderate Mardom Salari noted the "contradictory views" of Majlis Speaker Ali Larijani on the instability of the exchange rate. On Tuesday Mr Larijani told the Fars news agency: "Eighty percent of our economic issues and problems are related to the system of management."