Radical Shia cleric Moqtada Sadr has appealed for calm among Iraqi Shias following bomb attacks in Baghdad which killed about 50 people on Sunday.
Sadr's Mehdi Army has been playing a security role in Sadr City
Mr Sadr said Iraq was now in a state of civil war, but he said he would order his Mehdi army militia not to respond.
The bombings destroyed street markets in the slum district of Sadr City which is a stronghold of Sadr supporters.
He said US-led forces were responsible for letting the attacks happen but the government should maintain security.
"Sunnis and Shias are not responsible for such acts, national unity is required," Mr Sadr told reporters at his headquarters in Najaf.
Iraq has been experiencing a surge in sectarian violence since a bomb attack on an important Shia shrine in Samarra last month.
Mr Sadr also criticised US Defence Secretary Donald Rumsfeld who had said last week that Iraqi troops, not US forces, would intervene if civil war broke out in Iraq.
"May God damn you," Mr Sadr said of Mr Rumsfeld. "You said in the past that civil war would break out if you were to withdraw, and now you say that in case of civil war you won't interfere."
Following Sunday's attacks, President Jalal Talabani said in a statement: "The way in which this bloody act was conducted leaves us with no doubt that the terrorists have targeted this peaceful neighbourhood in order to ignite civil strife and stoke the fire of civil war."
He called on political parties to accelerate efforts to form a government, nearly three months after elections.
Sunday's bomb victims were buried after identification
A BBC correspondent in Baghdad says Sunday's attacks were seen not only as a provocation against the Shias, but also as a direct challenge to Mr Sadr's militia, which has been playing a security role in co-ordination with Iraqi police.
Associated Press reported that four bodies were found hanging from electricity pylons in Sadr City on Monday morning.
Police were quoted saying the dead men's identities were unknown, but residents said they had been arrested on Sunday in possession of explosive belts and mortar tubes by Mehdi Army members.
Elsewhere, there were reports of bombings in Taji, just north of the capital, which killed one person and injured six others, and in Iskandariyah, south of Baghdad, which killed a civilian.
Two car bombs exploded in Kirkuk within minutes of each other, killing one person and wounding 12 others.
US forces reported the death of an American marine on Sunday in fighting in the west of Iraq.