U.S. troops are facing what the military describes as spotty resistance in Tikrit, the hometown of deposed Iraqi leader, Saddam Hussein. U.S. Marines are now reported to have reached the center of the city.
U.S. forces used artillery and helicopter gunships in support of their drive to take control of Tikrit.
Reporters travelling with the troops say the Americans encountered resistance from ground troops on the outskirts of the city.
In one incident on Sunday, five Iraqi tanks moved south from Tikrit to attack the advancing American column. All five were destroyed. There are no reports of any U.S. casualties.
The resistance has been described as only spotty but the commander of U.S. forces, General Tommy Franks, told American television Sunday that it would be premature to declare the war over.
General Franks said, "We know that there are pockets of, I've heard 'em referred to as everything from paramilitary to death squad to Fedayeen Saddam. We know that there are pockets of that, we also know that there are pockets of foreigners who have decided to fight to their last breath and so until we have a sense that we have all of that under control, then we probably will not characterize the initial military phase as having been completed and the regime totally gone."
The Arabic news channel Al Jazeera reports a group of men representing local leaders are ready to negotiate the transfer of control of Tikrit to U.S. forces. They say Iraqi troops and the paramilitary Fedayeen Saddam left the city several days ago.
On the way to Tikrit, U.S. forces came upon seven U.S. soldiers who had been listed as missing or prisoners of war. They told their rescuers they were treated roughly when captured, but were given medical care.
The seven were flown to Kuwait, where they were examined by U.S. military doctors and reported to be in good condition.
Speaking on NBC's "Meet the Press" television program Sunday, U.S. Defense Secretary Donald Rumsfeld said local residents provided information about the prisoners' location. Secretary Rumsfeld said, "An awful lot of Iraqis are being cooperative. And in this case, they advised us that there were Americans in a certain location."
In Baghdad there were more firefights overnight as U.S. forces continued to engage Saddam Hussein loyalists. Marines battled a small group of armed men in a building near the Palestine hotel where international journalists are staying. Four men were taken into custody.
The looting which broke out in cities across Iraq after the departure of the old regime appears to have died down somewhat. VOA correspondent Alysha Ryu says U.S. troops in Baghdad have increased security measures, setting up checkpoints in several parts of the city.
Ryu said, "The looting that has gone on with the ministries and the hotels and embassies in that area, that has diminished considerably. People seem to have taken what they wanted and are no longer in that area. Of course, the security is much higher today than it has been in the last couple of days."
The United States says it will administer Iraq until a temporary Iraqi civilian authority can be constituted. Retired U.S. General Jay Garner, who will run the temporary U.S. administration, said the United States will create conditions for Iraqis to run the country themselves.
General Garner said, "What we're going to do and what we intend to do is create an environment inside Iraq so they can build a nation for themselves."
On Tuesday, a meeting is scheduled to be convened in southern Iraq to begin discussions on setting up an Iraqi interim authority. In an interview with British television, U.S. Secretary of State Colin Powell denied that anyone has been pre-selected to run that authority.
Secretary Powell said, "The United States has not anointed anyone to be the future leader of Iraq or to be the leader of the IIA, the Interim Iraqi Authority. We believe very strongly that the Iraqi people and representatives of the Iraqi people in the first instance are the ones who should do that. The president (Bush) has made it very clear that we are not in the business of installing the next president of Iraq."
There are sharp divisions in U.S. policymaking circles about whether controversial exile leader Ahmad Chalabi should head the interim authority, or whether someone else should have that job.