US forces have thrust into the heart of Baghdad as the 17-day-old war to topple President Saddam Hussein moved into a decisive new phase.
"We now do have troops in the city of Baghdad, we've moved right up the middle," a US military spokesman said on Saturday.
"We've seen some sporadic fighting throughout the night and we're continuing to move right up into the heart of the city," Captain Frank Thorp told MSNBC television.
"The members of the first Marine Expeditionary Force and the V Corps continue to take the fight to the enemy. We're taking opportunities to move forward," he said.
Thorp said US forces had clashed with a small number of Iraq's elite Special Republican Guard and the Marines had "penetrated" the Nida Division of the Republican Guard.
There was no immediate comment from the Iraqi authorities.
The push into central Baghdad followed a blistering overnight air and artillery barrage against its eastern flank.
US military sources said at least 20 Abrams battle tanks and 10 Bradley fighting vehicles rumbled up a southern highway through the city's Dawra suburb before swinging west and linking up with troops around the airport southwest of the city centre.
As the fighting came ever closer, many people fled in cars packed with blankets and belongings, apparently heading out of the city, Reuters correspondents reported.
The mood in the capital was grim.
"This is it. This is the final battle. We have no way out. We are facing a reality now. We're confronting the mightiest army in the world. What can we do? Where can we go? We're at a loss," said Nour Khaled, 48, a mother of two.
At least five blasts rocked a central area in the morning. Among targets hit was the previously bombed al-Mamoun communications centre, one of Baghdad's biggest.
Artillery fire reverberated through the night after US forces seized the international airport, 20 km (12 miles) southwest of the centre on Friday in a dramatic victory that drew an Iraqi threat to retaliate in unconventional style.
Iraq has denied that U.S.-led troops are closing in, describing those at the airport as an "isolated island".
US commanders moved to beef up their presence at the airport overnight, calling in soldiers from the 101st Airborne Division and the 94th battalion to reinforce the 3rd Infantry Division which spearheaded the attack on the facility.
The extra troops brought the number of American soldiers at the airport to about 1,500. There was no sign there of the "nonconventional" attack or "martyrdom operation" threatened by Iraqi Information Minister Mohammed Saeed al-Sahaf on Friday.
Iraqi officials say thousands of Arab volunteers are ready for suicide missions against US and British forces.
An Iraqi military communique read on television on Saturday said: "The enemy attacked our position near Baghdad last night," and it was defeated by army and Fedayeen paramilitary units.
In an apparent effort to rally the Iraqi people, state television showed footage of a man it said was Saddam touring the streets of his bombed capital on Friday.
Smiling, he greeted mobs of chanting admirers, smoke rising from fires burning in the distance. Some people kissed him on his cheeks and hands and he held up a small child. "We'll defend you with our blood and souls, Saddam," one man told him.
Outside the capital, a US officer said on Saturday that first tests of a white powder found in thousands of boxes indicated it was not a chemical weapon.
"On first analysis it does not appear to be a chemical that could be used in a chemical weapons attack," said Colonel John Peabody, commander of the Engineer Brigade of the 3rd Infantry Division. He said 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.
Secretary of State Colin Powell said in an interview published on Saturday there was no desire to besiege Baghdad.
"We hope there will be no siege. I don't know how they will carry out a siege and I don't think they will implement it by closing off a city whose residents total five million people," he told the London-based Arabic language al-Hayat newspaper.