Roger Hardy has some analysis:
The crackdown in Basra is fraught with political significance, writes the BBC Middle East analyst Roger Hardy.
Sadrists are convinced it is an attempt to weaken them ahead of provincial elections due in October - elections they are confident will strengthen their grip on the south.
Mr Maliki has embarked on a highly risky strategy, our analyst notes.
For one thing, it is far from clear that it will succeed.
The Sadrist movement enjoys widespread support, especially among the young and the poor, and is well entrenched in Basra and many other predominantly Shia towns and cities in the south.
For another, if the ceasefire which the Sadrists have largely followed since last summer were to collapse, that would seriously undermine claims by the government - and by the Bush administration in Washington - that Iraq had somehow turned a corner and was moving from civil war to political reconciliation. -- news.bbc.co.uk
I would agree, this one has a real pucker factor. Stay tuned.