THE STREETS OF TEHRAN…. Political unrest in Iran was relatively quiet throughout the fall, after the striking protests of the summer in the wake of the dubious Ahmadinejad election. But Iranians once again took to the streets over the weekend for protests that renew doubts about the future of the country’s ruling regime.

The intense clashes in several Iranian cities that left at least five protesters dead and scores more injured Sunday have raised the stakes for both sides as the government seeks to contain a newly revitalized opposition movement.

The street battles took place on one of the holiest days in the Shiite Muslim calendar, a fact that is likely to give even deeper resonance to Sunday’s deaths and that could help spawn further demonstrations in the days ahead. Opposition Web sites reported that as many as 12 protesters had been killed, including the nephew of defeated presidential candidate Mir Hossein Mousavi. The government conceded there had been five deaths in Tehran but denied responsibility and said the police had not used their weapons.

That account conflicted with those of numerous opposition sources, which reported that security forces had at various points opened fire on the crowds. Witnesses also reported that demonstrators, who numbered in the tens of thousands, fought back with unusual force, kicking and punching police officers and torching government buildings and vehicles. […]

Amid thick smoke from fires and tear gas that blanketed key parts of the city, Tehran became the scene of hand-to-hand combat between security forces and the protesters. At one point, according to witnesses, members of the pro-government Basij militia fired their handguns while ramming a car through two barriers set up by demonstrators. Elsewhere, the protesters, who in recent months had run whenever security forces moved in to disrupt demonstrations, began to attack riot police, pelting them with rocks and setting some of their vehicles ablaze.

The White House denounced the “violent and unjust suppression” of Iranian protestors. In a statement, White House National Security Council spokesperson Mike Hammer said, “Hope and history are on the side of those who peacefully seek their universal rights, and so is the United States.”

One of the bigger concerns, in the very near future, is that the Iranian government’s response to the protests will be even more severe than they were in the summer. Predicting an even harsher crackdown, Hamid Reza Jalaeipour, an opposition supporter and a sociology professor at Tehran University, said, “Everything will, from now on, be harsher, tougher, stronger.”

If yesterday’s events were any indication, this kind of response will only intensify the underlying conflict.

What’s more, Joe Klein highlighted the likely reaction from the “increasingly skeptical religious community in Qum” to the government’s brutality: “The only real hope for an end to the Revolutionary Guards’ dictatorship is broad opposition by the mullahs. No one knows whether that is possible, but today’s violence surely makes the current regime’s moral standing less tenable.”

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Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.