Rival visions of how to halt the carnage in Iraq went on show Tuesday as US troops built walls around a restive suburb of Baghdad and a Shiite leader announced a plan to set up local militias.
In Baghdad, US and Iraqi forces are trying to restore the battered authority of Iraq's coalition goverment by sweeping city districts for weapons and isolating protected areas behind checkpoints and concrete barriers.
But in the holy city of Najaf - which was last week the scene of a deadly bomb attack outside a major Shiite shrine - local leaders said they would take matters into their own hands and authorise neighbourhood militias.
"We started today forming a committee in Najaf to choose individuals who will control security in their neighbourhoods and keep an eye on all suspicious movements in their areas," deputy governor Abdul Hussain Abtan said.
"This will be done in collaboration with security forces in the city and is the first step in activating popular committees," he said, in a move which will be seen as a snub to the government of Prime Minister Nuri al-Maliki.
Abtan belongs to a powerful Shiite party, the Supreme Council of Islamic Revolution in Iraq (SCIRI), whose leader Abdel Aziz al-Hakim had called for "popular committees" to take over security after Thursday's bombing.
Hakim's supporters argue that Shiite communities must be allowed to protect themselves from attacks carried out by so-called "takfiris", Sunni extremists angered by the fall of Saddam Hussein and opposed to the US-backed government.
Since February, when suspected Sunni bombers destroyed the golden dome of a holy Shiite mosque in Samarra, insurgent bomb attacks and sectarian death squads have killed thousands of Iraqis in a string of tit-for-tat massacres.
Tempers were further raised last Thursday, when a bomber got to the last checkpoint before the entrance to the shrine of Imam Ali in Najaf and detonated his explosive vest, killing 35 people, including Shiite pilgrims.
Violent attacks killed 13 Iraqis on Tuesday, including one soldier and two policemen, according to a tally of police and medical reports.
The government's US backers, however, fear that Shiite neighbourhood watch groups would become power centres to rival the government and eventually even a kind of "state within the state" on the model of Lebanon's Hezbollah.
Part of the capital, the impoverished Shiite suburb of Sadr City, is already largely under the control of the Mehdi Army militia of radical cleric Moqtada al-Sadr, whose fighters have fought with US forces in the past.
And, in another sign of the danger posed by Iraq's private armies, police clashed Tuesday in the Shiite city of Kerbala with militiamen loyal to a lesser known cleric, Ayatollah Mahmoud al-Hasani.
Police imposed a curfew on Kerbala after fighting broke out between security forces and militiamen. A city medical official said one Iraqi soldier was killed, while five policemen and one civilian were wounded.
US commanders fear that mounting sectarian violence and the proliferation of local militias could push Iraq into all out civil war, and have launched their own drive to protect vulnerable populations.
In Baghdad, the joint US-Iraq operation "Together Foward" has brought 10,000 US troops and 50,000 government security forces on to the streets of the city.
On Tuesday, the US military said the Dura district of southern Baghdad had been walled in behind concrete barricades and fortified check points.
All vehicles in the neighbourhood are to be stopped by Iraqi police looking for "terrorists, bomb-making materials and illegal weapons," a statement said.
The statement added that Dura "is not being sealed off as a result of attacks on coalition forces, but because it is being used by terrorists to incite sectarian tension between Sunni and Shiite Muslims".