UPDATE Thursday, July 9–Clashes erupted today between at least a thousand protestors in Tehran and baton-wielding security forces. Demonstrations took place all over Iran — according to one report, in 400 cities.

In Iran, a supposed sandstorm is being used to create its own “fog of war.”

The Iranian opposition called for a three-day general strike to demonstrate their rejection of President Ahmadinejad, and in response the Iranian government ordered the shutdown of all banks, businesses, and universities because of a sandstorm.

And Thursday could be the start of a new street confrontation, if reports of a planned march that day are true. The Los Angeles Times reports that the opposition has called for a protest march on Thursday, to commemorate the tenth anniversary of the 1999 regime crackdown on student protestors. The call comes after a prolonged period of relative calm in the streets, and that they are urging marchers to carry roses:

Keep quiet under all circumstances, the circular advises those planning to march in Thursday’s unauthorized demonstrations in Iran cities.

“The heaviest weapon to carry is one rose in the hand,” it says.

As Iranians prepare for what could be another violent day of confrontations Thursday between demonstrators and security forces, including pro-government plainclothes Basiji militias, supporters of opposition candidate Mir-Hossein Mousavi have distributed instructions to try to keep any anticipated violence to a minimum.

The Wall Street Journal reports:

The three top leaders of Iran’s opposition joined forces on Tuesday and their supporters began a three-day national strike, signaling a resurrection of protests. … Opposition candidates Mir Hossein Mousavi and Mehdi Karroubi, joined by former President Mohamad Khatami, met to plot strategy and issued their first-ever joint statement, calling for an end to the government’s arrests and what they called “savage, shocking attacks” on their advisers and supporters. …

Simultaneously, Iran’s government on Tuesday announced an unexpected public holiday for 48 hours due to emergency level of pollution and a dust storm covering the capital. Some speculated that it could be an attempt to mask the impact of the public strikes.

The government ordered all industries and businesses in the capital to remain shut and only vehicles with emergency business to come out, though Tehran often faces high-level pollution and the dust storm is reported to be worse in cities to the south and east.

The nightly shouts of “God is great!” and “Death to the dictator!” continue to echo from rooftops, in what has become the opposition’s signature protest, and there are reports that the leaders of the opposition are calling for other steps, too, including spraying green paint on walls around the capital. (Green was the color chosen by Mousavi’s campaign to rally its supporters.)

At the Monday meeting with Karroubi and Khatami, Mousavi declared that the “the government [of President Mahmoud Ahmadinejad] lacks legitimacy as it does not have the nation’s vote,” according to Iran’s PressTV. But Mousavi and his allies are wary of provoking a showdown in the streets, and he added: “We should make every effort to pursue the case of our opposition by moving within a legal framework.”

Karroubi, speaking to campaign supporters, added: “A government which takes over the wheel of the country without popular vote has no legitimacy and this reality gets more and more evident day by day.”

As the opposition stands firm, the centrist bloc led by Ali Akbar Hashemi Rafansjani seems to be standing with them. One day after Rafsanjani met in public with relatives of those arrested in the post-election crackdown, his political party issued a defiant statement:

“We declare that the result is unacceptable due to the unhealthy voting process, massive electoral fraud and the siding of the majority of the Guardian Council with a specific candidate.”