In a move that could signal the beginning of the end — the final and most difficult stage of Operation Iraqi Freedom — the U.S. Army's 3rd Infantry troops and U.S. Marines entered Baghdad Saturday.

Coalition troops went all the way to the heart of the Iraqi capital, smashing through Republican Guard units as they charged into the city.

"It was a clear statement of the ability of coalition forces to move into Baghdad at the time and place of their choosing," Maj. Gen. Gene Renuart, operations director at U.S. Central Command, said after the troops returned to the outskirts of the capital.

The intent, Renuart said in a briefing at Central Command in Qatar, was to show the Iraqi leadership "that they do not have the control they speak about on their television."

• Maps: Iraq | Baghdad

Late Saturday, low-flying aircraft were heard over Baghdad. Moments later a huge explosion resounded across the central part of the city, shaking buildings, including the Palestine Hotel where foreign journalists still in Baghdad are staying.

A column of 26 American tanks and 10 Bradley fighting vehicles from the 3rd Infantry, 2nd Brigade, entered the city in the morning and engaged Republican Guard troops and paramilitary forces, Fox News' Greg Kelly reported. Fox broadcast exclusive video of the drive into the capital, showing images of burning vehicles near a deserted highway through a desolate stretch of land.

Coalition forces also were surrounding Baghdad to prevent reinforcements from entering, Renuart said.

"[It's] essentially isolation," he said. "We'll continue to operate with our forces around the city to prevent forces from coming into the city and challenging us," he said. 

A senior U.S. military official said allied troops have seized several objectives at multiple points surrounding Baghdad, including areas north and northwest of the city. The official declined to identify which sites had been taken.

Preparing for Urban Combat

Allied warplanes began flying missions specifically designed to prepare for any future ground attack on downtown Baghdad, said Lt. Gen. Michael Moseley, the U.S. Air Force general in charge of the air war.

Moseley, speaking from his command post in Saudi Arabia, said he hoped that the Iraqi regime would surrender before urban warfare became necessary.

But as of Saturday, a wide variety of aircraft had begun performing the mission of "airborne forward air controllers" to direct airstrikes in the event ground forces begin fighting in the center of the city. Mosely said the planes are flying on both sides of the Tigris River, which runs through the capital.

Red Cross workers in Baghdad reported several hundred war wounded and dozens of dead had been brought to four city hospitals since Friday, the International Committee of the Red Cross said. The ICRC could not say how many were civilians.

"The hospitals are finding it increasingly difficult to cope with the continuous influx of wounded," the ICRC's Muin Kassis said Saturday in Amman, Jordan.

President Bush, in his weekly radio address, praised the American troops and said liberation for the Iraqi people is near.

"No crime of this dying regime will divert us from our mission," the president said. "Village by village, city by city, liberation is coming."

Making a 'Clear Statement'

The U.S. incursion was not an attempt to capture large sections of Baghdad, which remained under tenuous Iraqi government control. Rather, Renuart said, "it was a clear statement of the ability of coalition forces to move into Baghdad at the time and place of their choosing."

Navy Capt. Frank Thorp, a coalition spokesman, said U.S. forces had entered "the heart of Baghdad."

Renuart described only a brief sweep by one unit in and out of the capital. He declined to say if any troops remained inside, though U.S. military officials — speaking on condition of anonymity — later said several unspecified objectives had been seized on the north and northwest edge of the city.

Iraqi TV played patriotic music, and soldiers and militiamen loyal to Saddam Hussein vowed to keep fighting. Renuart said the American armored unit encountered "pockets of very intense fighting" from Republican Guards and irregular fighters using rocket propelled grenades and air-to-air artillery weapons.

Thousands of U.S. troops had gathered on Baghdad's outskirts — the 3rd Infantry Division arriving from the southwest and the 1st Marine Expeditionary Force from the southeast.

The Iraqi military, in a statement read on satellite television, said U.S. forces were repulsed when they tried to advance on Baghdad from the south. "We were able to chop off their rotten heads," the statement said.

On the southern outskirts, Marines engaged in close-quarters fighting with pro-Saddam volunteers from Jordan, Egypt, Sudan and elsewhere, according to Lt. Col. B.P. McCoy of 3rd Battalion, 4th Marines.

"It's like a jihad. They were given a rifle and told to become a martyr," said McCoy, whose troops used bayonets while battling in the reeds of a marsh.

Civilians Wave White Flags

As other Marine units advanced north, Iraqi civilian vehicles fled south, packed with bundles and bearing improvised white flags made from torn-up towels or T-shirts.

Explosions and machine-gun fire could be heard across Baghdad, and armed Iraqis in pickup trucks and police cars raced through the streets. Members of the Fedayeen, a militia led by Saddam's son Odai, appeared in downtown for the first time since the war began, identifiable by distinctive black uniforms.

Long lines at gasoline stations underscored a sense of crisis in a city that has been without power since Thursday night. At markets, vendors did a brisk business selling batteries and flashlights.

At Baghdad's airport, captured by U.S. troops Friday, soldiers used explosives to clear abandoned buildings and examined an extensive underground complex below the airfield.

Lt. Col. Lee Fetterman, a battalion commander with the 101st Airborne Division, said several hundred Iraqis were killed at the airport, including some with bombs strapped to them who apparently intended to attempt suicide attacks.

Renuart said the Americans' hold on the airport was firm, despite Iraqi counterattacks Saturday, and he indicated one runway would soon be usable.

Iraqi Official Claims Victory

Iraqi Information Minister Mohammed Saeed al-Sahhaf, on the other hand, contended the Americans had been ousted from the airport.

"Today, we butchered the force present at the airport," al-Sahhaf said. He also indicated that Iraqi fighters would stage "creative operations," including suicide attacks.

Southwest of the capital, units of the 3rd Infantry captured the abandoned headquarters of the Republican Guard's Medina division — one of Saddam's best-trained units — in the town of Suwayrah. Outside the base were dozens of artillery pieces, anti-aircraft guns, tanks and armored personnel carriers.

Overnight, Coalition aircraft struck the residence of Ali Hassan al-Majid, infamously known as "Chemical Ali." Al-Majid, who is Saddam's cousin, is notorious for ordering Iraqi forces to use chemical weapons on Kurds in northern Iraq.

Two Coalition aircraft using laser-guided munitions struck al-Majid's home in Al Basrah, about 250 miles southeast of Baghdad.

As U.S. forces entered Baghdad, there was no definitive word on Saddam's whereabouts. A statement attributed to him Saturday, read by al-Sahhaf, urged Iraqi fighters to destroy the "lost and shocked" enemy.

'Saddam Hussein Is No Longer a Factor'

An Iraqi television broadcast Friday showed Saddam — or someone posing as him — greeting civilians in the streets of Baghdad and giving a defiant speech. A reference in the speech to a downed U.S. helicopter was interpreted by American intelligence officials as a sign Saddam probably did survive a missile and bombing strike intended to kill him on the opening night of the war.

"Saddam Hussein is no longer really a factor in this war," said Group Capt. Al Lockwood, a spokesman for the U.S.-British forces. "If we capture Saddam Hussein alive, so be it. We will put him on trial for war crimes. But if he is not alive, that will not affect the way we carry out this campaign."

Though U.S. casualties in the attack on Baghdad have been light, two Marine pilots were killed Saturday when their Super Cobra attack helicopter crashed in central Iraq.

Also, the Pentagon confirmed the first combat death of an American woman in the war — Pfc. Lori Ann Piestewa, 23, of Tuba City, Ariz. Her body, and those of six colleagues from the 507th Maintenance Company, were found during the rescue of American POW Jessica Lynch in Iraq this week. Their unit was ambushed March 23.

The Arab television network Al-Jazeera, sometimes criticized for its coverage by U.S. officials, carried a report Saturday about American soldiers' efforts to provide fresh water for beleaguered civilians in the city of Nasiriyah.

The Associated Press contributed to this report.