Police in Iraq's holy city of Karbala have ordered Shi'ite pilgrims to leave the city after two days of violence surrounding a major religious festival left dozens of people dead and injured. Reporter Cache Seel has details from our Middle East bureau in Cairo.

Gun battles raged and emergency vehicles sped through the streets of Karbala near the Shi'ite shrines at the center of celebrations marking the ninth-century birthday of the last Shi'ite imam. The festival was to have reached its climax late Tuesday and Wednesday morning.

It was not immediately clear what caused the fighting, some blamed scuffles caused by stringent security measures, others said Shi'ite militias were to blame.

Shi'ite religious processions have often been marred by violence, usually by Sunni extremists who believe the Shia to be apostates.

The worst such incident was in 2005 when nearly 1,000 pilgrims were killed in a stampede caused by rumors of a suicide bomber on a Baghdad bridge. In Karbala, nearly 100 people were killed this past April in car bombings aimed at Shi'ite shrines. 

Waleed Kazziha, the director of the department of political science at the American University in Cairo, says that in addition to threats from Sunni extremists, friction between the two largest Shi'ite militias added to the already volatile situation in Karbala.

"I think this was inevitable that something of this magnitude, this festival of that magnitude that it would not be utilized or exploited by each of these parties to its own advantage and ultimately ends up in a rupture," he said.

The violence began Monday when pilgrims, frustrated by standing in long lines at security checkpoints, began pelting police with rocks. It dramatically escalated Tuesday with reports of gun battles and mortar attacks.

Iraqi officials have provided buses to evacuate pilgrims. More troops and police are being sent to attempt to restore peace.

In other news from Iraq, the U.S. military says Iraqi and coalition forces killed 33 insurgents in a joint operation Monday north of Baghdad. A military statement says the operation reopened a major irrigation canal that had been seized by gunmen.

Iraq's political factions have made fresh attempts to restore peace on the national level. Sunday, representatives from Iraq's three main factions - Shi'ite, Sunni, and Kurd - reached a power-sharing agreement. Details of the agreement have not been made public, except a clause allowing Baath party loyalists from Saddam Hussein's Sunni-dominated regime to return to working for the government.

Alex Bigham, an Iraq analyst with London-based Foreign Policy Center, says the agreement is a positive step, but not enough on its own to satisfy Iraq's Sunni minority.

"That is welcome. That was the key request of some of the Sunni parties in order to become more involved in Iraqi politics," said Bigham. "Of course, many of the Sunni groups rejected the constitutional referendums and did not participate in the elections, so that is certainly welcome, but there are a number of other criteria that have to be met."

But the negotiations did not include Iraq's largest Sunni bloc, the Sunni Accordance Front that has boycotted the government since early August. The group praised the initiative, but said it will not return until reforms are implemented.