US President George W Bush has insisted that the "violent and ruthless" insurgency in Iraq will be defeated.
Bush said the US was laying the foundation for peace in the world
After talks in Washington with Iraqi PM Ibrahim Jaafari, Mr Bush said the political progress that was being made in the country would lead to victory.
He said US troops would eventually withdraw "with honour", but declined to set a timetable for withdrawal.
His comments came after six US troops were killed in a suicide car bombing in the Iraqi city of Falluja.
Three of the casualties were servicewomen. At least 13 other people were injured in the attack - 11 of them women.
The White House has announced that Mr Bush will make a prime-time address to his nation about Iraq next Tuesday, amid growing concern about the level of US casualties.
"The enemy's goal is to drive us out of Iraq - they will not succeed," said the president.
"It's tough work and it's hard. But nevertheless, progress is being made... and the progress that is being made will lead to the defeat of this enemy."
That progress included January's elections, forming a government appointing Mr Jaafari as prime minister.
Mr Jaafari said Iraq's new government was making "steady and substantial progress" with the help of the US.
Baghdad has been struck by a series of bombings this week
"This is not the time to fall back... we owe it to those who have made sacrifices to continue towards the goals."
He called on Mr Bush to help to rebuild Iraq in a project on the same scale as the Marshall Plan which was drawn up after World War II for the reconstruction of Germany.
Both men said they expected an agreement on a new constitution for Iraq by an August deadline.
The BBC's Jon Leyne in the Iraqi capital Baghdad says the problem for the Americans and for the Iraqi government is that the political advances are having no impact on the violence - in fact, there has been an upsurge in attacks since the new Iraqi government took office.
He adds that although Iraqis are continuing to volunteer for the new security forces in large numbers, there is no sign that the Iraqis are any nearer being able to take control of their own security - the key to President Bush's long-term strategy.
Mr Bush and Mr Jaafari's meeting came after a recent opinion poll suggested that 51% of Americans now think the invasion of Iraq two years ago was a mistake.
Separately, former Iraqi Deputy Prime Minister Tariq Aziz, who is awaiting trial in an Iraqi jail, has said he will not testify in court against former Iraqi leader Saddam Hussein.
Speaking through his lawyer, Mr Aziz also said he wanted a trial on "independent soil".
"My client told me that he was in good health and spirits, and the medical treatment offered to him is improving, despite his more than two-year detention," lawyer Badi Aref Izzat told CNNArabic.com.
The lawyer repeated that "any interrogation or future trial, if there is any evidence against Mr Aziz, should be conducted on an independent soil, such as Holland or Sweden".