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Deafening explosions rocked central Baghdad early Sunday as Iraqi troops, members of President Saddam Hussein's Fedayeen militia and teenage soldiers patrolled streets to protect the capital from U.S.-led forces.

U.S. armor penetrated the city early Saturday for the first time, but quickly moved out and headed toward the airport on Baghdad's western edge, U.S. Central Command officials said.

With the Americans trying to send the message they can strike anywhere, Iraqi leaders maintained a bold front.

They denied U.S. troops had entered the capital and claimed Saddam's forces had retaken the airport -- killing hundreds of American "scoundrels," the military said.

"Today, the tide has turned," Information Minister Mohammed Saeed al-Sahhaf said. "We are destroying them." He read a statement from Saddam telling Iraq's fighters to rush at the Americans and "exhaust (them) and increase the depth of their wounds."

Al-Sahhaf said the Americans were in the suburbs and in a message on television urged residents to inform Iraqi troops about any U.S. movements. Maintain "calm, good organization ... to confront the enemy effectively, conquer it, and force it to retreat accursed and defeated," he said.

By Saturday night, city streets were crawling with all kinds of armed men -- government troops, militiamen, loyalists from Saddam's Baath party. Members of the Fedayeen, a militia led by Saddam's son Odai, appeared in their distinctive black uniforms in the city center for the first time since the war began.

Armed with Kalashnikovs, mortars and heavy machine guns, soldiers of the elite Republican Guard Corps dug fresh trenches and fortified old ones. Some took over houses close to the city's southern approaches.

Government-owned Iraqi television showed footage Saturday of Saddam meeting with his sons Odai and Qusai, although it was unclear when the meeting took place.

Low-flying aircraft were heard over the city Saturday, followed by huge explosions that shook city buildings. More explosions and the sounds of artillery shelling continued early Sunday.

But for most of the night, Baghdad was relatively quiet. The drone of aircraft flying overhead was frequently heard, but there was no anti-aircraft fire. At around 6 a.m. Sunday, there was a series of loud explosions.

During the day Saturday, Iraqi tanks, armored personnel carriers and field artillery were deployed in the capital, facing the western, southern and northern entrances that U.S. forces were believed most likely to use.

"I am not afraid to die," said 16-year-old Thamer Mekki, an eighth-grader in blue jeans and a T-shirt who says he learned how to shoot a gun at age 14.

"I am doing this for my country," said Mekki, standing guard in the upscale Mansour district.

U.S. troops traveled north into the capital Saturday, turned west at the Tigris River, then out of the city and toward the airport, military officials said. During the sweep, the Americans came under intense fire from Republican Guards with small arms and rocket-propelled grenades.

Earlier in the day, clouds of black smoke darkened the skies from trenches of oil set on fire 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 Salhiya -- making a roaring noise as they headed south.

On the city's southern outskirts, 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.

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

Power returned to most of Baghdad on Saturday, two days after the city went dark.

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.

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.

Iraqis got into long lines at gasoline stations, although some shops, including a small store that sells birds, remained open. Hawkers of batteries and flashlights were doing brisk business in the fabled Shorja market in the city's center.

There were also some signs of panic.

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