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. 

U.S. troops penetrated the city early Saturday for the first time, traveling north into the capital and turning west at the Tigris River, out of the city and toward the airport, a U.S. Central Command spokesman said.

A reporter touring the city of 5 million by car at midday saw no coalition soldiers. Asked at a briefing why no reporters had spotted them, the spokesman, Maj. Gen. Gene Renuart, suggested that in a city so big, it was easy to miss them.

"I'm pretty comfortable that in some parts of downtown London you can't see what is going on in other parts of downtown London," he told a British reporter. "I can't give you any better answer than that."

Clouds of black smoke darkened the skies from trenches of oil set alight as a defense, but a steady stream of cars and buses passed through the plaza in front of Baghdad's large, ornate Mosque of the Unknown Soldier.

Several rockets were launched from a truck in the central Baghdad district of al-Salhiya — making a roaring noise as they headed south. The rumblings of explosions could be heard throughout the city, growing ever louder as they shook buildings.

Information Minister Mohammed Saeed al-Sahhaf held his usual midday news conference, telling reporters that U.S. troops were not in the capital and claiming Saddam's forces had retaken the airport.

"Today, the tide has turned," al-Sahhaf said. "We are destroying them."

Later, al-Sahhaf read a statement from Saddam urging his men to charge coalition forces "and destroy them." The statement maintained U.S.-led troops tried to attack Baghdad because they "found themselves lost and shocked" in battles against Iraqi forces, guerrillas and the people.

On the southern outskirts of Baghdad, the burned out hulks of at least two Iraqi armored personnel carriers and two all-terrain vehicles sat along the main highway heading south. Many armed men, some in civilian clothes, headed toward southern districts of the city, hitchhiking for rides to the front.

There was no sign of any fighting on the road, up to about nine miles south of the city center.

On the northern and northeastern districts of the city, army tanks could be seen at major intersections. Armored personnel carriers with troops on top roamed the streets.

Some new sites were hit by coalition bombs overnight, including the National Assembly across the street from the al-Rasheed Hotel and a police headquarters in central Baghdad and the telephone exchange of al-Maamoun.

Elsewhere in the city, police cars moved in groups in two or three with sirens squealing and occupants flashing "V for victory" signs, carrying portraits of Saddam and waving Iraqi flags.

There appeared to be fewer armed men on downtown streets than about a week ago. But members of Saddam's Fedayeen, a militia led by Saddam's son Odai, appeared in the city center for the first time since the war began. They were easily identified in distinctive black uniforms.

Speaking to the Al-Arabiya Arab satellite channel, a man who claimed to be a member of the Fedayeen vowed to keep up the fight.

"They are cowards. They cannot face us on the ground. They control the sky, but we are able to confront whoever goes on the ground," said the man, who covered his face with a red-checkered keffiyah to conceal his identity.

Knots of soldiers clad in Republican Guard uniforms, distinctive by their red triangular insignia, patrolled the southern outskirts of Baghdad around the neighborhood of Baladiya.

Bombing and artillery fire sounded throughout that area, anti aircraft guns and mortars lined the southern entrance to the city, but they were mostly off the road away from the main road — the most likely entry point of American forces.

The U.S. military said it had already penetrated deep into the capital.

"As of this morning, coalition forces are actually in the city of Baghdad," said Navy Capt. Frank Thorp. "As we moved into the city, we saw sporadic fighting, we've actually moved through the Republican Guard divisions to pretty much the center of the city."

Throughout the morning, armed men in pickup cars dashed across Baghdad at high speed.

Long lines at gasoline stations underscored the sense of crisis. Some shops were still open. In the fabled Shorja market, also in the heart of Baghdad, hawkers selling batteries and flashlights were doing brisk business. Curiously, a small store that sells birds was open.

Some signs of panic were becoming evident, however.

Armed men ran toward an area where a rumor said a coalition pilot had parachuted into the city center. The gunmen's cars screeched to a halt. They jumped out of the vehicle, Kalashnikovs at the ready, and sprinted to an area among high-rise apartment blocks in central Baghdad. There was no indication that the report was true.

On Friday, the capital's defenders prepared to make their last stand — digging ditches and stocking up on ammunition.

At the same time, thousands of frightened residents fled in bumper-to-bumper traffic. They packed buses, trucks, pickup cars, taxis, private cars — even horse-drawn carts — with blankets, foodstuffs, furniture, heaters, television sets, pillows, stoves, cooking pots, mattresses and pillows.