Iran's feared Revolutionary Guards warned of a decisive confrontation if protestors came out today. More than 1,000 people defied them before security forces delivered on their threat.
"Police were beating protestors with batons and shooting into the air to scare them off," one Iranian dissident said by telephone.
On his Web site, opposition leader Mir Hossein Mousavi urged the protestors on. But he hasn't been seen in public for days, leaving opposition supporters disorganized.
"Today's protest wasn't organized in advance," said a dissident. "People weren't well informed."
Disagreement over the election extends to the highest levels of the Iranian government. On Sunday, the parliamentary speaker said the government should listen to the protestors' demands, after the supreme leader dismissed those concerns on Friday.
There are doubts about the election even among Iran's most senior clerics.
"The fact that the clerics have given the election no official recognition is significant. …The regime is divided within," said Roger Cohen of the New York Times, one of a handful of western reporters still in Iran.
In the headlines of official newspapers and in public statements, Iranian leaders point to a foreign hand in the protests.
"Western powers and western media are spreading anarchy and vandalism," said Hassan Qashqavi, Iran's foreign ministry spokesman.
Mousavi's Web site called Monday for supporters to turn on their car lights in the late afternoon as a sign of protest.
A student leader in Iran told ABC News the opposition is planning to close the main Tehran bazaar on Tuesday, shutting down many businesses. It would also have big symbolic importance.
President Obama Monday said he has good reason to continue to issue measured criticism of Iran's election turmoil. "The last thing that I want to do is to have the United States be a foil for those forces inside Iran who would love nothing better than to make this an argument about the United States," Obama said in an interview on the CBS broadcast "The Early Show."
Press Secretary Robert Gibbs said Obama still has "questions and concerns'" about the election and "has been moved what we've seen on television. I think particularly so by images of women in Iran who have stood up for their right to demonstrate, to speak out and to be heard."
The White House announced today Obama would hold a news conference Tuesday.
Iran conceded today there were voting problems, in as many as 50 cities, saying that the total number of votes in some of these areas outnumbered the number of eligible voters.
State-run Press TV reported on its Web site that as many as 3 million extra votes could have been cast, but according to a spokesman for Iran's Guardian Council, that would not be enough to affect the outcome of the controversial election in which President Mahmoud Ahmadinejad was declared the winner.
But it is a potentially significant comedown for a regime that has dismissed all election fraud charges.
In the statement the Guard told demonstrators to "end the sabotage and rioting activities" and described the protests as a "conspiracy" against Iran.