Updated

Allied forces carried out a massive bombing campaign on Baghdad early Friday, smashing telecommunications structures in the Iraqi capital in an attempt to cut off Saddam Hussein from his military and civilians.

A B-2 bomber dropped two large, satellite-guided "Bunker Buster" bombs -- each weighing 5,000 pounds -- on a major communications tower on the east bank of the Tigris River in downtown Baghdad.

They were the largest bombs used so far in Operation Iraqi Freedom.

• Map: The War in Iraq

The attack gutted a seven-story telephone exchange building in an area called Al-Alwya, leaving the street strewn with slabs of concrete, irons rods and corrugated metal.

"Coalition air forces and Tomahawk missiles took out a communications and command and control facilities in the capital city during the night," said U.S. Central Command spokesman Lt. Cmdr. Charles Owens.

The bombing of Baghdad also targeted positions of the estimated 30,000 Republican Guard troops who are ringing the city.

Witnesses said air strikes hit a ruling Baath party office, killing eight people. Two paramilitary headquarters were also destroyed, and Iraq's satellite television channel has been cutting in and out since the attacks.

Husein Moeini, telecommunications director of Baghdad, said people were buried beneath the rubble, but journalists who arrived at the scene less than three hours later didn't see a rescue operation under way.

Thunderous explosions rocked Baghdad on Friday and a towering column of churning orange smoke rose over the skyline after a break in the weather opened the way for the mightiest bombardment of the Iraqi capital in days.

"We haven't had anything that's hindered our operations to date," Brig. Gen. Vincent Brooks said during a Central Command briefing. "Our morale is very high."

Defense Secretary Donald H. Rumsfeld suggested that U.S. forces might not rush to conquer Baghdad, but instead may lay siege to the capital and hope the 5 million Iraqis rise up against the government.

Iraqis Shoot at Civilians Fleeing Basra

British officers reported that a "couple of thousand" Iraqi civilians tried to flee Basra, which is encircled by British troops, but were chased back into the city by mortar and machine gun fire from Iraqi paramilitary forces.

British forces hope to eliminate units still loyal to Saddam and open the way for badly needed humanitarian aid in the city, which has a population of 1.3 million.

There have been reports of significant numbers of civilians coming out of Basra daily to get food and then returning.

British soldiers from the 1st Black Watch battalion were trying to wedge themselves between the Iraqi gunmen and the targeted civilians, while others tried to evacuate civilians and treat casualties.

"Our interpretation of this is ... here perhaps are the first pieces of evidence of Iraqi people trying to break free from the Baath party regime and the militia," British military spokesman Col. Chris Vernon told Sky News. "And clearly the militia don't want that. They want to keep their population in there, and they fired on them to force them back in."

Deputy Defense Secretary Paul Wolfowitz, responding to criticism of the allies' preparation for the fight, said Friday at the Foreign Press Center: "I don't think you can say we underestimated the strength of resistance, but I think we did underestimate the extent of the regime's willingness to commit war crimes."

Saddam Still in Control

The bombing assault came as sources told Fox News that U.S. government officials have all but concluded that Saddam remains in control of his military and is preparing for the battle of Baghdad.

Saddam is believed to be issuing orders as he moves from one underground bunker to the next.

The Iraqi regime breathed defiance even as coalition troops encircled its capital city.

"The enemy must come inside Baghdad, and that will be its grave," said Defense Minister Sultan Hashim Ahmed.

Iraqi Information Minister Mohammed Saeed al Sahhaf said 75 civilians had been killed and 290 wounded in U.S. and British bombardments overnight, including seven deaths in Baghdad. He also said Iraqi forces destroyed or damaged several allied vehicles and killed four soldiers in an attack on a convoy near Najaf, less than 100 miles south of Baghdad.

Sahhaf rejected allied contentions that Iraq planned to use chemical weapons -- speculation that arose after advancing forces found protective suits and gas masks left behind by retreating soldiers. Sahhaf said having such equipment is standard for any army.

In the War Zone

On the battlefield, as sporadic battles rage between American infantry and defiant Iraqi troops and paramilitary guerrillas, more armor and at least 25,000 reinforcing allied troops are on the way.

American Army and Marine infantry forces are arrayed to the south of Baghdad, some within 50 miles of the capital. They are led by the Army's 3rd Infantry and 101st Airborne divisions and the 1st Marine Expeditionary Force.

Coalition special operations forces are working both in western and northern Iraq, and the Army's 173rd Airborne Brigade has secured an airfield in the north with 1,000 paratroopers. More are on the way.

Special forces have cleared large areas of western Iraq, ensuring Saddam's forces cannot launch missile strikes on neighbors such as Jordan, Saudi Arabia and Israel.

About 90,000 U.S. troops are inside Iraq, a senior defense official said, adding that was an increase of about 14,000 in just two days. More than 250,000 U.S. troops are in the region, including thousands aboard Navy ships at sea, on air bases in surrounding countries and at headquarters encampments.

More Troops on the Way

Another 100,000 to 120,000 ground troops have received deployment orders and are expected to begin arriving in Kuwait in coming days, including the Army's 4th Infantry, 1st Armored and 1st Cavalry divisions.

Fox News learned Thursday night that 2,000 Marines were shifted from anti-terrorism duty in the Gulf of Aden to Operation Iraqi Freedom.

Warplanes bombed positions in northern Iraq near Kurdish-held areas and hit Republican Guard forces menacing American ground forces 50 miles south of Baghdad.

Combat aircraft dropped bombs "just about as fast as we can load them," said Capt. Thomas A. Parker, aboard the USS Kitty Hawk in the Persian Gulf.

In central Iraq, the first resupply plane landed on a restored runway at Tallil Airfield -- hastily renamed "Bush International Airport" by American forces.

Still, Iraqi resistance continued to slow the drive on the capital and kept coalition forces out of key cities such as Basra and Nasiriyah.

Central Command said Friday that four Marines with the 1st Marine Expeditionary Force are currently unaccounted for after battles in this region. Names are being withheld pending notification of their families.

Maritime units cleared mines near the port of Umm Qasr to clear the way for ships bringing humanitarian aid.

Coalition forces have increased communication broadcasts in Iraq to include television in all of southern Iraq, as well as in Baghdad and the surrounding areas. They also have radio broadcasts running regularly. British forces have begun operating an AM radio station out of Umm Qasr.

Brooks said the Iraqis have been developing missile and other weapons systems with longer ranges. The Iraqis have been taking about one shot a day at neighboring Kuwait.

Fox News' Mike Tobin and Carl Cameron and The Associated Press contributed to this report.