The Iranian regime has taken the gloves off. They have deployed overwhelming force to block access to the planned gathering places in Tehran and are meeting the scattered thousands of protestors who try to get through with batons, tear gas and fire-hoses.
The protestors have taken a more belligerant turn as well. Slogans of "death to the dictator" are more common now, as is "death to Khameini". Over the past week, the focus of the protests has been on the disputed election results, and the opposition has been overtly against Ahmedinejad, not Khameini. But the Supreme Leader's harsh rhetoric during his Friday sermon has drawn a line in the sand that today's protestors seem willing to cross.
Shortly after the clashes began, official state media reported that a suicide bomber struck the Imam Khomeini mausoleum. There has been widespread speculation among Iranian tweeters that the government itself blew up the mausoleum in order to blame the protestors and justify harsher measures against them. The mullahs did something similar 30 years ago, setting fire to a crowded cinema and blaming the Shah. Western media has pointed out that the mausoleum bombing has not yet been independently confirmed.
I don't think Mousavi can stop the protests now, even if the government convinces him to do so. He is reportedly giving a speech now, but I have not yet seen reports of its content. The government's harsh treatment of its citizens has created new opposition. I do not believe they will be satisfied with a new election now. Nothing short of the removal of Khameini will satsisfy them. The mood has changed. Martin Luther King will give way to Bobby Seale.