US President George Bush has vowed that the US will deal harshly with Iraqis who attack American troops, insisting his forces will not pull out.
The rebuilding of Iraq is on track, the US claims
"There are some who feel like the conditions are such that they can attack us there. My answer is bring them on," Mr Bush said.
"We've got the force necessary to deal with the security situation."
At least 18 US soldiers have been killed since Mr Bush declared major combat operations over on 1 May.
In Baghdad, one of six US soldiers wounded in two separate attacks on Tuesday has died of his injuries.
Six British soldiers were killed in a single incident last month.
Road to democracy
On a visit to Baghdad on Wednesday, UK Foreign Secretary Jack Straw said the attacks increased London's and Washington's determination to root out remnants of Saddam Hussein's regime.
Mr Bush - who on Tuesday said the US faced a massive and long-term undertaking in Iraq - promised that those who attacked US troops would be "found and brought to justice".
He said he would welcome help from other countries willing to send troops, but said the US had "plenty tough force" to restore order in Iraq.
"The enemy shouldn't make any mistake about it, we will deal with them harshly if they continue to try to bring harm to the Iraqi people," he said.
He also condemned militant attacks on Iraqi power lines and other infrastructure.
Mr Bush's comments came amid controversy over what caused a huge explosion that killed lat least nine people at a mosque in the town of Falluja, including the imam.
US military authorities said a bomb-making class inside the mosque triggered the explosion
Local residents have accused the Americans of causing the blast with a missile.
The BBC's Justin Webb in Washington says senior politicians of the main US political parties have been pressing the White House to be clearer about the nature of the commitment the US is going to have to make if Iraq is to be put on the road towards democracy.
The pressure comes as opinion polls show a marked decline in the number of Americans who are convinced of the success of the Iraq campaign.
The latest - carried out by USA Today, CNN and Gallup - found that 56% of respondents thought things were going well for US forces in Iraq - a drop from 70% a month ago and 86% in the second week in May.