Baghdad awoke Monday to the scream of missiles, the thud of artillery shells and the crackle of heavy machine gun fire. Buildings in the city shook violently and black smoke shrouded the air.

Armored columns of the 2nd Brigade of the 3rd Infantry division entered the city about 6 a.m. with more than 70 tanks and 60 Bradley fighting vehicles. Col. David Perkins told his troops the operation was intended to be "a dramatic show of force" that U.S. troops can enter Baghdad at will. The troops also raided the city's Al-Rashid Hotel, and Perkins said another palace on the eastern side of the Tigris also was under attack.

"I hope this makes it clear to the Iraqi people that this (regime) is over and that they can now enjoy their new freedom," Perkins said.

In another action weighted with symbolism and tactical importance, a hulking U.S. C-130 transport plane landed at the Baghdad international airport Sunday. The arrival presaged a major resupply effort by air for U.S. troops, dependent until now on a tenuous line stretching 350 miles to Kuwait.

U.S. officials declared Baghdad cut off from the rest of Iraq.

"We do control the highways in and out of the city and do have the capability to interdict, to stop, to attack any Iraqi military forces that might try to either escape or to engage our forces," said Gen. Peter Pace, vice chairman of the Joint Chiefs of Staff.

Marines closing in on Baghdad from the south were told to take off their protective suits Monday for the first time in 20 days, a sign of easing fears of possible use of chemical or biological weapons.

Intense fighting took a growing toll on combatants and civilians. Injured Russian diplomats and a convoy of America's Kurdish comrades in arms were among unintended victims caught in crossfire and friendly fire Sunday. Kurds said 18 of their own died in the mistaken U.S. air strike.

Assorted prizes fell into allied hands, some after hard fighting, but U.S. forces had yet to confront Baghdad's last-ditch defenders on a large scale.

"They are extremely weakened, but that does not mean they're finished," Pace said of the Republican Guard.

Inside a VIP building at the airport, troops found a lavish hideaway believed to have been used by Saddam, Associated Press Television News reported.

Southeast of Baghdad, Marines seized one of Saddam's palaces, poked through remnants of a Republican Guard headquarters and searched a suspected terrorist training camp, finding the shell of a passenger jet believed to be used for hijacking practice.

Also to the south, U.S. forces on took control Sunday of the center of the holy city of Karbala, the Army Times newspaper reported from the scene.

Monday's push into Baghdad was the third straight day that U.S. troops entered the city.

There was no sign of Iraqi troops except for a group seen running northward. Two Iraqi tanks sat motionless. Iraqi troops did not use any mortars or artillery against the American forces.

U.S. forces also made armored raids into the city on Sunday, testing Iraqi defenses and destroying all of the Iraqi vehicles and fighters they came in contact with, U.S. officials said.

A statement broadcast on Iraqi state television in Saddam's name was typically defiant but hinted at problems coordinating the nation's defense. It urged soldiers who had been separated from regular units to join up with any unit they could find.

Pace said the Republican Guard's main weapons systems are gone and the force probably cannot assemble more than 1,000 men in any one place.

On another vital front, British troops thrust to the center of Basra, Iraq's second largest city, with a sense they were finally shaking Saddam loyalists loose.

British Desert Rats went into the city of 1.3 million with more than three dozen tanks and armored cars, a column similar in size to the American unit that probed suburban Baghdad, then got quickly out. But the British found resistance softer than expected, picked up reports that the local Baath Party leadership was crumbling and fought into the core, losing at least three soldiers and finding their arrival cheered by hundreds of citizens.

"We have a lot of it occupied," British Maj. Gen. Peter Wall told the BBC. He said it might take days to put down renegades.

In chalking up military gains, the United States accelerated a campaign of persuasion, too, aimed at getting the Iraqi Republican Guard to give up. And Washington's attention began turning to postwar Iraq.

Pace said the United States would welcome Republican Guard division commanders and troops in a postwar government if they surrendered now.

"I mean, there's a small clique around Saddam Hussein who are the perpetrators of all the crimes against humanity," Pace said on ABC's "This Week."

"Below them are still many senior leaders and troops who have their free will to decide what their life is going to be like. They can surrender and become part of the future free Iraq, or they can fight and die."

The United States is deploying some of Iraq's exiles and internal dissidents around the country to help root out pro-Saddam elements, keep order and distribute aid, according to one such organization, the Iraq National Congress. The group said several hundred of its members were flown to an area near the city of Nasiriyah.

Deputy Defense Secretary Paul Wolfowitz said it will probably take more than six months once the war is over before a new Iraqi government can take over.

In northern Iraq, U.S. warplanes struck a convoy of allied Kurdish fighters and U.S. special forces Sunday in one of the deadliest friendly fire attacks of the war. At least 18 people were killed and more than 45 wounded, including senior Kurdish commanders, Kurdish officials said.

U.S. Central Command only reported one civilian killed and six people injured, including a U.S. soldier, but its investigation was not complete.

A convoy of Russian diplomats, including the ambassador, came under fire Sunday while evacuating Baghdad, the Russian foreign ministry said. A correspondent for state-run Russian television said the convoy was caught in a crossfire and three diplomats were hurt, one with a serious stomach wound.

U.S. Central Command said no allied forces were operating in the area at the time, but it was investigating what happened.

In and around Baghdad, civilians were caught up in the intensified ground fighting.

At the al-Kindi hospital in a working-class Baghdad district, scores of civilians with shrapnel wounds have been coming in since Saturday night. Among them were eight members of one family.

In one ward, several children wore bloodstained casts on their legs and arms, and some had difficulty breathing. One girl had bandages over half her face.

British tasted a breakthrough in Basra against Saddam's hard-core militia.

"Their days are limited," said Brigadier Graham Binns, commander of the Desert Rats. "Our intelligence tells us that morale is low among the defenders of the city, that the population can't wait to see us, and the opposition such as it is, is uncoordinated."

Central Command officials estimated Sunday that 2,000 to 3,000 Iraqi fighters died in the 3rd Infantry Division's 25-mile incursion in an industrial section of Baghdad a day earlier.