Kurdish paramilitaries said they would hand over the important oil hub of Kirkuk to US troops later on Friday. The rich city, traditional capital of the Kurds, fell on Thursday to a mixed force of Kurdish guerrillas and US Special Forces.
In Baghdad, Reuters correspondent Sean Maguire heard a fierce fire fight rage for about an hour in the northeast of the capital before quiet settled on the city again around dawn.
There were no immediate details of the latest battle with Iraqi fighters holding out in isolated pockets of Baghdad despite the collapse of Saddam's 24-year rule.
But rampant looting and violence in Baghdad, the murder of a Shiite religious leader in the holy city of Najaf and a suicide bombing at a Baghdad checkpoint on Thursday highlighted the problems US troops face in restoring order in the chaos engulfing Iraq.
Humanitarian organisations criticised the US troops, saying the failure to prevent looting and anarchy threatened their efforts to provide desperately needed assistance.
Two days after US forces drove tanks into the heart of Baghdad, Saddam's whereabouts were still unknown.
Cities fall in north
US troops sent in reinforcements to take control of the strategic prize of Kirkuk, which provides 40 percent of Iraq's oil revenue. Hundreds of dejected Iraqis were seen walking south from the city.
The Kurds have promised to leave Kirkuk, helping to calm Turkish alarm after the Kurdish "peshmerga" militia took it over in a largely bloodless rout of Iraqi forces.
"Yes, we expect to be leaving when the Americans arrive, and that may well be later today," said Mam Rostam, a Kurdish commander whose forces had rushed into Kirkuk, apparently without the full agreement of Washington.
"The city of Kirkuk will be in the hands of American and coalition forces," said Jalal Talabani, leader of the Patriotic Union of Kurdistan, one of the two main Iraqi Kurdish parties.
Ankara fears the Kurds could use the city's wealth to finance an independent state and stimulate separatist demands by Turkey's large Kurdish minority.
A Kurdish commander at a checkpoint just outside Mosul said fighters loyal to Saddam had fled. A Reuters reporter who drove into the city said there were no Iraqi fighters to be seen.
US planes bomb home of Saddam's half-brother
US forces pressed on with efforts to hunt down deposed Iraqi leaders.
A US aircraft hit the residence of Barzan Ibrahim Hasan al-Tikriti, Saddam's half-brother and former head of Iraq's Mukhabarat intelligence service, with six "smart bombs".
The results of the attack on the building, which was also an operations centre for the intelligence service, were not yet known. There was no indication US forces thought Saddam might be in the house near Ramadi, 110 km (70 miles) west of Baghdad.
In Najaf on Thursday, Iraqi Shi'ite leader Abdul Majid al-Khoei and an aide were stabbed and shot to death in a mob attack in the gold-domed Imam Ali Mosque, the city's holiest shrine. The killings seemed certain to widen divisions and sow hatred among Shi'ites, who are 60 percent of the population.
Abdul Majid returned to Iraq only last week but his presence provoked intense criticism from other Iraqi Shi'ite dissidents keen to assert their authority after the fall of Saddam.
A suicide bomber detonated explosives at a US checkpoint in the capital on Thursday evening. "Some are dead in the attack but I don't know how many," Marine officer Matt Baker told Reuters. A Pentagon spokesman said four soldiers were wounded.
A Marine was killed hours earlier and more than 20 wounded in a battle with Saddam loyalists firing from the Imam al-Adham Mosque on the eastern bank of the Tigris river.
In the three-week war prior to the latest losses, US forces had suffered 105 dead. Another 11 were listed as missing. Thirty British troops have been killed. There is no authoritative estimate for Iraqi military and civilian casualties but they certainly run into the thousands.
The immediate problem facing American troops in Baghdad was quelling remaining pockets of resistance and restoring law and order.
Looters carted off bottles of wine and whisky, guns and paintings of half-naked women on Thursday from the home of Uday, Saddam's feared playboy son. They also picked clean his yacht and made off with some of his white Arabian horses.
Severe looting has also raged in the southern city of Basra, now under the military control of British troops.
Aid officials said US and American troops were obliged by international law to prevent chaos.
"The picture is a very dark one. There is absolutely no security on the street," said Veronique Taveau, spokeswoman for the UN Office of the Humanitarian Coordinator for Iraq.
"There is widespread looting and every official building and most of the UN compounds have been looted. Humanitarian assistance will be hurt."
The International Committee of the Red Cross said one hospital in central Baghdad had been attacked by armed looters and others hospitals had been closed.
US President George W. Bush promised Iraqis the United States and its allies would help end the chaos.
"Coalition forces will help maintain law and order, so that Iraqis can live in security," Bush said in a taped message.
The United States is trying to organise a meeting of Iraqi opposition leaders in the next few days to start the process of selecting an interim government.
Meanwhile, a humanitarian effort to bring food and other supplies to Iraq was beginning. Pentagon spokeswoman Victoria Clarke said a British ship unloaded more than 200,000 tons of food, water and medicine at the port of Umm Qasr.
The United States has still not confirmed finding any of the weapons of mass destruction it says Iraq had been hiding - the issue which prompted the invasion.