America's overseer in Iraq, Paul Bremer, has pledged to bring to justice the killers of four US contractors whose bodies were mutilated by a mob.
Iraq saw new attacks and attempted attacks on Thursday
A senior US official said coalition forces would return to the flashpoint town of Falluja and hunt down those responsible for the killings.
An ambush on a US convoy near the town on Thursday injured several US troops, but Falluja itself appeared to be calm.
A major trade fair due to open in Baghdad on Monday has been postponed.
Correspondents said an eerie silence reigned in Falluja on Thursday - no US troops were in sight in the town.
Residents went about their normal daily business, while burn marks on the main street were the only trace of the attack.
28 April 2003: US paratroopers shoot dead 13 demonstrators
May 2003: Grenade and gun attacks on US troops become a routine occurrence
November 2003-January 2004: Three helicopters are shot down in the area with the total loss of 25 lives
31 March 2004: Four US contractors killed and mutilated
Some residents said they would not let American forces into the city.
One, Ahmed al-Dulaimi, said there would be "hell" if they tried to enter.
"Yesterday's attack is proof of how much we hate the Americans," said another, Sameer Sami.
The remains of the four dead American contractors have been retrieved by Iraqi police and handed over to US forces.
The private US firm which employed the contractors, Blackwater Security Consulting, said it would not release the victims' identities out of respect for their families.
Speaking in Baghdad, Mr Bremer said the deaths of the Americans and their "despicable" mutilation - recorded by cameramen - would not "derail the march toward stability and democracy" in Iraq.
General Mark Kimmitt, deputy head of coalition operations, said coalition forces "will respond" to the attack.
"They are going to hunt down the people responsible for his bestial act.
"It will be at a time and a place of our choosing. It will be methodical, it will be precise and it will be overwhelming," he said.
The BBC's Nick Childs at the Pentagon says the nature of the attacks has clearly provoked outrage among US military officials and a rethink of tactics in Falluja.
But, he says, Pentagon officials acknowledge it remains a difficult balancing act - how to put on an effective show of strength without appearing to overreact?
The contractors were ambushed and killed as they drove through Falluja, triggering scenes which have shocked America and fuelled debate over the cost of the conflict in Iraq.
The bodies were dragged from the wreckage, hacked to pieces and two of them were hanged from a bridge.
US television networks led their news bulletins with the Falluja story but showed only edited pictures of the grisly scenes, with the bodies blurred.
The much-anticipated US-sponsored Destination Baghdad Expo trade fair due to open on Monday was postponed indefinitely following the attacks.
More than 200 companies from over 26 countries were scheduled to participate in what was expected to be the first fair of its kind in post-war Baghdad.
Organisers said the decision was taken after reviewing security, and comes days after the US consular office in Baghdad warned those attending that their safety could not be guaranteed.
"US citizens are... reminded that 9 April is the first anniversary of the US military entry to Baghdad," a state department notice reportedly said.
Elsewhere in Iraq on Thursday, six Iraqis were killed in a car bombing at a market in Ramadi, near Falluja.
An Iraqi was killed in clashes between police and unpaid workers in Basra in the south.
Gunmen near Kirkuk in the north wounded one policeman at a checkpoint while abducting a second.