The Sunni-led "Anbar Awakening" gets most of the attention and credit for what security improvements have happened in Iraq. Often overlooked is the importance of a cease-fire between the Mahdi Army, led by Shiite cleric Muqtada al-Sadr, and on the other side, U.S. forces and the Iraqi government. That cease-fire now seems in danger of imminent dissolution -- that is, if it has not ended already. Though al-Sadr renewed his pledge in February, he has reportedly been under pressure from senior members of his organization to lift it, and two weeks ago he issued a declaration allowing his loyalists to fire on U.S. and Iraqi government troops in self-defense. The latest round of fighting seems to be bringing tensions to the breaking point; al-Sadr called for nationwide civil disobedience on Monday, and Sadrists in parliament walked out on Tuesday.

Rockets were fired from the Sadr City neighborhood of Baghdad into the city's Green Zone Tuesday -- according to the Christian Science Monitor, that's the third time in two days such an attack has occurred. Firefights have occurred in Baghdad between the Mahdi Army and a combination of U.S. and Iraqi government forces. And, according to the Washington Post, "Sadr's movement led a labor strike for a second day in many parts of eastern and central Baghdad on Tuesday, demanding the release of Sadr's jailed followers and an end to Iraqi government raids. Sadrist leaders ordered stores to close and taxi and bus drivers to stop operations. Many neighborhoods turned into virtual ghost towns, their usually busy streets all but empty. Parents kept their children home from school."

Meanwhile, Iraq's second-largest city, Basra, is the location of a major offensive against Shiite militias, especially the Mahdi Army. Iraqi Prime Minister Nouri al-Maliki and his defense and interior ministers are personally commanding the Iraqi troops who have been dispatched. (Reports on just how many Iraqi troops are involved vary, with most estimates saying 15,000, but the New York Times is reporting almost 30,000.)

As Time's Joe Klein observes, the operations in Basra are not without complications of their own. "The Iraqi Army in Basra is mostly composed of another renegade militia -- the Badr Corps, an organization founded by Iran and answerable to ISCI -- the Shi'ite faction led by the Hakim family, Sadr's great rival," Klein writes. In a 2007 interview I did with journalist Martin Smith, who had just returned from Iraq, where he made a documentary for PBS about the influence of sectarian militias, Smith said something similar:

After the January 2005 elections, there were a number of firings of Sunni leaders in the Ministry of the Interior, and Badr Corps [the militia unit of the SCIRI, a Shiite political party] people were brought into leadership positions, and there was a definite sectarian taint for many police units. Whole units were brought in intact from the Badr militia, according to some accounts that we were told. How one goes out and establishes all of this is problematic, but there are numerous reports of whole units of Badr Corps coming intact into the ministry to work in the police forces.

(The name of the Hakim family organization has changed several times; SCIRI is an old term. It now uses ISCI, for Islamic Supreme Council of Iraq.)

And from various media reports, it seems that Sadrists aren't staying quiet about the sectarianism inherent in the Basra offensive. Before the Sadrists walked out of parliament, McClatchy reports, they had "condemn[ed] the operation as a political move to hand the south to Abdul Aziz al Hakim, the head of the [ISCI]." A Mahdi Army commander told the Times, "The U.S., the Iraqi government and Sciri are against us ... They are trying to finish us. They want power for the Iraqi government and Sciri."

The cease-fire still technically remains in effect, but it's unclear how long that will last. The Christian Science Monitor reports on one Mahdi Army militiaman in Baghdad who, reached by phone, said, "The cease-fire is over; we have been told to fight the Americans." The CSM reports that in January, that same man was abiding by the cease-fire.