You've got to hand it to the thugs running Iran. They learned a thing or two about how to break up demonstrations during the last go around with the reformers and have applied the lessons with vigor.
Thousands of opposition supporters have clashed with security forces in the centre of the Iranian capital, Tehran.
Police used tear gas and detained dozens rallying in solidarity with uprisings in Egypt and Tunisia. There was one report of a death in Tehran.
The BBC also received reports of similar protests being held in the cities of Isfahan, Mashhad and Shiraz.
Earlier, the police placed opposition leader Mir Hossein Mousavi under house arrest, according to his website.
It said the move was intended to prevent the former prime minister attending the march in Tehran, which the authorities had prohibited. The road leading to Mr Mousavi's house was also blocked by police vans.
Fellow opposition leader Mehdi Karroubi, a former speaker of parliament and a senior cleric, is also reportedly under de facto house arrest.
The situation got ugly, quickly: CNN reports:
Uniformed security forces and pro-government Basij militiamen had earlier advanced on crowds who chanted "Death to the dictator!" during demonstrations in the city's Imam Hossein Square -- the planned starting point of a scheduled rally, a witness said.
"We definitely see them as enemies of the revolution and spies, and we will confront them with force," said Cmdr. Hossein Hamedani of the Revolutionary Guard, according to the official Islamic Republic News Agency.
Thousands of security personnel lined Revolution Avenue, allowing the march to continue but preventing the marchers from congregating in Azadi Square -- considered a rallying point by opposition groups.
"You can't take two steps without running into security personnel," one witness said. "They're all over the place."
Several protesters who were diverted by police to side streets were beaten with batons and gassed by security officers who were waiting at those locations, witnesses said.
That the protestors were able to organize at all is a testament to the adage "Where there's a will, there's a way." It takes more than guts to join a protest these days in Iran - as evidenced by what happened to so many after the last go around:
The opposition says more than 80 of its supporters were killed over the following six months, a figure the government disputes. Several have been sentenced to death, and dozens jailed.
Can the Iranian opposition rev up the demonstrations again? They may try, but unlike Egypt, Iran has the state security apparatus that would have no problem massacring their own people - the basij and the Revolutionary Guards. It will take a lot of moxie to participate in protests when you know the security forces could open fire at any time.