The power of the Shia and Sunni militias presents the Iraqi government with one of their most challenging problems. BBC Arabic.com asked a number of Iraqis how the militias affected their lives.
OMAR ALI MOHAMMED, 18, BAGHDAD
My second name is Ali, which is a Shia name. My first name is Omar, a traditionally Sunni name.
A militiaman from the Shia Mehdi army
My mother liked the idea that through my name I was reflecting both the Sunni and the Shia traditions, despite the fact that we are Shia.
It turns out her decision to call me Omar was not a good one.
My name is not to the liking of either Shias or Sunnis, and I was nearly killed recently because of it.
During my exams, I had to travel between my mainly Sunni neighbourhood to a Shia district. As always, there were militias belonging to each sect on the outskirts of each area.
As I was about to enter the Shia area, an armed militiaman stopped me.
He asked me to show him my ID card. The militiamen saw my name, and they asked me whether I was Shia or Sunni.
I told them that I was Shia, but my mother called me Omar to bring the two sects closer. They started beating and kicking me severely because they thought I was a liar, and they told me that if they saw me again, they would kill me.
Either I change my name, or I leave the country altogether
The same thing happened to me at the hands of Sunnis, because my father's name is Ali. I narrowly escaped being killed.
It is strange, I do not feel that I belong to either side. I am Shia by birth, but I have always seen myself as an Iraqi. I have always been proud of my name which unites the two sects.
There is no solution. Either I change my name and accept being forced to take sides, or I leave the country altogether. Now, I am even afraid to leave the house.
KHALID, 29, BAGHDAD
I live in Talbiya, a Shia area, very close to Sadr city.
Our neighbourhood is currently under the control of the Mehdi army, one of the most powerful Shia militias.
The Mehdi army is made up of ordinary people who took matters into their own hands after the regime collapsed and they saw that the government was not doing anything to protect them.
These individuals now play a major role in our area.
You see them driving expensive cars and carrying arms. People go to them for help and protection.
The militias are becoming indispensable to us because they provide us with protection.
I agree that militias play a negative role, but given the weakness of the police, army and the state of lawlessness, we find ourselves forced to rely on them.
For example, the militias helped a family to get their son released after he was kidnapped by militias in another area.
The militias have an effective intelligence network, and they know everyone in the area.
They are becoming indispensable to us because they provide us with protection.
MOHAMMED, POLICEMAN, BAGHDAD
The role of the militias often does not conflict with that of the police at all.
I cannot call them outlaws; there is no law
For example, you see militiamen helping traffic police in their work, and they also help in deterring thieves and burglars.
Merchants and grocers used to be very frightened of sending their goods to be sold in Jamila market, one of the biggest vegetable and fruit markets in Baghdad.
But now there are no thieves in Jamila market, thanks to the militias.
I cannot call these men outlaws, because there is no law in the first place. They are people whose existence is dictated by the lawlessness and chaos in Iraq.
ABU MUSTAFA, DOCTOR'S ASSISTANT
I have been living in this mainly Shia neighbourhood for 20 years.
Although I am Sunni, I haven't suffered any ill-treatment in this area, even after the increase of sectarianism in the country.
People in my area come to me for medical help any time day or night.
However, I think that the existence of militias is a problem.
Mehdi army militiamen in Baghdad
I fear that I may be attacked if the Shia militias in the area were to be provoked by Sunni militias.
One day I found a threatening note pinned to my door warning me to leave the neighbourhood. I took the note and I went to the militia's headquarters.
They told me that it was not their work, and asked me to call them should anything untoward happen. They assured me they knew me very well, and that they were aware that I helped people and that I did not behave in a sectarian way.
But I am not happy or comfortable that the militia have control.
The only authority that should carry arms is the government police and security, or else we will have chaos.
But for the time being, they make the place more secure, because the government is still weak.
KHALIDA, 40, BAGHDAD
I am a Shia woman living in Amariya, which is a mainly Sunni area in Baghdad.
The militias have turned our lives into a living hell
There were a large number of Saddam's senior army officers and many ex-Baath party senior officials living here; all of them made wealthy during the reign of Saddam.
After Saddam was toppled, most of them lost their power and privileges and they were struggling both financially and psychologically.
It was easy for them to join the pro al-Qaeda militias.
I told the neighbours that we were Sunnis, but after months of fear, I have decided to leave Iraq.
I have seen killings every day.
I saw with my own eyes young men being killed simply for being the sons of Shia families in the area.
I saw a 20-year-old girl being killed simply for having worked in a hairdresser's shop.
The militias have turned our lives into a living hell. They want us to live according to their laws and rules.
Young children are not allowed to wear shorts and western hairstyles are not permitted.