So What Did Go On In Najaf on Sunday?

I'm mystified, and I'm apparently not the only one based on various blog postings, including this from AJ at AmericaBlog:

I'm a little baffled by the news on yesterday's battle in Najaf. Outlets are breathlessly reporting that an attack on major Shia religious leaders, including Ayatollah Sistani (a "good" Ayatollah, for those keeping score at home), was foiled by Iraqi troops with American support. The lead of most articles is, of course, that 250 fighters were (reportedly) killed, but that's probably the least important element of the story.

The implication generally seems to be that there were Sunni insurgents in the outskirts of Najaf, a holy city in Iraq and the home of Sistani, in the operational stages of an attack on the city, including a major Shia mosque and Sistani himself. When I first read this, I was extremely skeptical. The insurgency is largely decentralized, including widespread reports of infighting, and even when they're able to cooperate on a large scale, insurgents largely use indirect fire (IEDs, mortars, etc.) -- rather than small arms fire (guns) -- against major targets. It sounded to me more like some kind of mass uprising of a particular group or sect.I wasn't surprised to read, therefore, that Arab press is reporting not one, not two, but three possible scenarios to explain the fighting.

One is the Sunni insurgent possibility, but the other two indicate that the fighters were actually Shia. As usual, Juan Cole is indispensable on the intricacies. One Shia narrative suggests an uprising after an attempt to arrest a radical Shia cleric; the other indicates the group consisted of "Twelvers" (sometimes referred to as millenarians) who sought to bring about the return of the Mahdi by assassinating the four main Najaf clerics.It is hard for me to understand why the identities of the fighters is still in question...a