Iraq's information minister has read a message he says was from President Saddam Hussein urging the Iraqi armed forces and ordinary citizens to step up attacks to defeat the US-led invasion.
"The criminals will be humiliated," Minister Mohammed Saeed al-Sahaf said, quoting from the message on the 17th day of the war. US forces said they sent troops on Saturday into the heart of Baghdad for a first time.
"To hurt the enemy more, raise the level of your attacks," Sahaf quoted Saddam as saying. The message said that the attackers were concentrating on Baghdad but were weakening elsewhere in Iraq.
Iraq denied any US forces were in Baghdad and said its troops had driven the Americans from the international airport - a claim that a US military spokesman said was groundless.
US military sources said at least 20 Abrams tanks and 10 Bradley fighting vehicles had rumbled up a southern highway through Baghdad's Dawra suburb before swinging west and linking up with troops at the airport southwest of the city centre.
A correspondent who drove freely around the sprawling city of five million later on Saturday saw no sign of US forces in areas he visited.
US Major-General Victor Renuart said the incursion had been a "clear statement of the ability of the coalition forces to move into Baghdad at times and places of their choosing".
He told a news conference in Qatar such operations would continue, adding: "This fight is far from over."
Information Minister Mohammed Saeed al-Sahaf, reading a message he said was from Saddam, said invasion forces were concentrating on Baghdad, but weakening elsewhere in Iraq.
Iraqi television showed footage on Friday of a smiling Saddam touring Baghdad streets, greeting admirers as smoke rose in the distance. It was not clear exactly when the footage was shot.
Renuart said he did not know if the man shown was Saddam and described the question as irrelevant. "The objective is to end the regime in Iraq and we'll continue with that," he said.
As US units operated in Baghdad, other troops protected their rear with a ground and air assault on the Shi'ite Muslim shrine city of Kerbala, 110 km (70 miles) to the southwest.
In the north, US forces moved from Kurdish-held territory towards Iraqi lines defending the oil city of Mosul, after a day of American air strikes on the area.
The US foray into Baghdad met resistance described by one spokesman as sporadic. "There were firefights, but if you're one of those folks who were involved in that firefight on the ground, it was pretty intense," Captain Frank Thorp said.
Four US soldiers were wounded, one of them shot in the head, and an Iraqi general was captured, US sources said.
Rocket-propelled grenades damaged one US tank. A second had to be abandoned in Baghdad because of mechanical failure.
US forces called in air support to attack Iraqi tanks on the northern edge of the airport, military sources said.
The Americans said they had won control of the airport, 20 km (12 miles) from the city centre, on Friday. They say they hold the runway, but not all outlying areas.
An Iraqi military spokesman said hundreds of US troops had been killed in the airport fighting.
A US Marine gunnery sergeant said on Saturday his unit had been told there had been a suicide bombing at the airport.
"The last order we just got said there was another suicide bombing at the airport, so be especially vigilant at roadblocks," Mark Woodward told correspondent Matthew Green, with the Marines southeast of Baghdad.
Renuart said he was aware of the report but was not aware of any suicide bombing at the airport.
U.S.-led forces have been on heightened alert for possible suicide attacks after two previous bombings killed a total of seven of their soldiers in Iraq.
The International Committee of the Red Cross said several hundred wounded Iraqis had been admitted to Baghdad hospitals after US troops reached the city and fighting erupted.
The push into Baghdad followed a blistering overnight air and artillery barrage against its eastern flank.
As the war came closer, many people fled in cars packed with blankets and belongings. The mood in the capital was grim.
"This is it. This is the final battle. We have no way out," said Nour Khaled, 48, a mother of two. "We're confronting the mightiest army in the world. What can we do? Where can we go?"
Hundreds of men, women and children were trudging south from Baghdad on a main road 20-30 km (12-19 miles) outside the city, Green reported. Most were empty-handed or carried children too young to walk in midday heat through open fields and marshlands.
To the north of the city, US military officials reported traffic jams as Baghdad residents fled.
In the Kerbala fighting, helicopter-borne troops of the 101st Airborne Division landed on the western edge of town and moved in beside a tank battalion with Apache attack helicopters overhead, correspondent Kieran Murray reported.
Iraqi paramilitary forces fired assault rifles and rocket-propelled grenades from city rooftops. US forces hit back using attack helicopters, artillery and heavy weapons.
"It's freaky in there. Lots of bullets flying around. It's pretty scary," said one US soldier who was among half a dozen troops wounded in the fierce street fighting.
US officers said fighter jets had hit a Republican Guard facility, the ruling Baath Party headquarters and an ammunitions depot with 2,000 pound bombs shortly before midday.
Three huge plumes of smoke rose above Kerbala and secondary explosions were heard after the air strikes.
Britain said there were signs of pressure building up on Iraq's government but the war was not over yet.
"(U.S.) tanks have gone into Baghdad to make it clear to the people that whatever the regime may say, coalition forces are advancing and there is a determination to see the job through," said a spokesman for Prime Minister Tony Blair.
South of Baghdad, a US officer said first tests of a white powder found in thousands of boxes showed it was not a chemical weapon. Colonel John Peabody told journalists most of it appeared to be the nerve gas antidote atropine, and another chemical.
Washington launched the war vowing to oust Saddam and rid Iraq of chemical and biological weapons. Baghdad denies having such arms and invasion forces have yet to find any.
The US military identified eight soldiers killed in the reported ambush of a supply convoy in southern Iraq on March 23, raising to 75 the number of American troops killed in the war.
The remains of the troops were found in a hospital in Nassiriya more than a week after the encounter by US special forces who rescued a captured woman soldier, Jessica Lynch.
Even before overthrowing Saddam's government, the United States will unveil the first stages of a civil administration for post-war Iraq in the next few days, a US official said.
Turkey ordered the expulsion of three Iraqi diplomats, but said the move was not related to US requests to 60 countries to shut down Iraqi missions.