A series of reports critical of U.S. combat operations in Iraq have emerged as the 10th anniversary of the invasion approaches.
State Department spokeswoman Victoria Nuland said the bilateral relationship with Iraq is been challenging but important.
"The challenges are complex," she said.
U.S. forces in 2003 invaded Iraq on the grounds that Saddam's weapons program was too great of a threat to ignore. No such weapons were found.
Special Inspector General for Iraq Reconstruction Stuart Bowen issued his final report to Congress last week. It said that Iraqi leaders questioned the net benefits despite a 10-year engagement that cost the United States $60 billion.
British think tank Chatham House added the "Iraq debacle" hurt Washington's credibility in the region.
Nuland said that bilateral affairs were more secure than during the Saddam era, however.
"Both countries have made enormous sacrifices to get us where we are and to start this new chapter but we're committed to Iraq for the long term and we're committed to its prosperity, its unity and integrity, and to its ability to be a strong democracy in the region," she said.