Coalition forces maneuvered through Baghdad with near impunity on Tuesday, a day after bombing a building where Saddam Hussein, his sons and other regime officials were believed to be meeting.

Senior U.S. officials told Fox News, "There's a strong chance we got Saddam and probably both sons." The officials said the CIA provided the intelligence that led to the strike and it was not immediately clear whether any leadership targets were killed or wounded.

One Air Force B-1B bomber was called in for the strike in a Baghdad suburb, defense officials told Fox News. The heavy bomber dropped four 2000-pound "bunker-buster" bombs.

• Maps: Iraq | Baghdad

Earlier, coalition officials said they believed Saddam's top commander in southern Iraq had been killed in a U.S. airstrike.

U.S. Marines entered the capital from the south and southeast early Tuesday, sending a contingent to guard a nuclear plant protected by large berms.

A large explosion rocked the area near the Palestine Hotel in downtown Baghdad, a location that has become a mainstay for much of the media covering the war in Iraq. U.S Central Command has confirmed to Fox News that a sniper was operating from a balcony in the Palestine Hotel. Central Command stressed that coalition forces only strike legitimate military targets, and that it is still unknown who is responsible for this incident.

Reuters reported that at least four journalists were injured in the blast, at least two of them severely. Abu Dhabi TV also reported that a Spanish reporter was killed from the explosion.

U.S Central Command has confirmed to Fox News that a sniper was operating from a balcony in the Palestine Hotel. Central Command stressed that coalition forces only strike legitimate military targets, and that it is still unknown who is responsible for this incident.

From Baghdad airport, the U.S. 101st Airborne division on Tuesday attacked an 8-story building about a half-mile away that had been used as a base for a small number of Republican Guard holdouts. American forces killed two Iraqis and suffered no casualties in the assault.

Iraqi resistance appeared to be melting away.

On Monday, some Iraqi soldiers jumped into the Tigris River to flee the advancing column of more than 100 armored vehicles. A dozen others were captured and placed inside a hastily erected POW pen on the grounds of the bombed-out, blue-and-gold-domed New Presidential Palace.

An estimated 600 to 1,000 Iraqi troops were killed during the operation, said Col. David Perkins. "We had a lot of suicide attackers today," he said. "These guys are going to die in droves ... They keep trying to ram the tanks with car bombs."

U.S. troops toppled a 40-foot statue of Saddam and seized another of his many palaces, the Sojoud. Tank-killing A-10 Warthog planes and pilotless drones provided air cover as Americans briefly surrounded another prominent symbol of Saddam's power, the Information Ministry, as well as the Al-Rashid hotel. Fighting resumed Tuesday morning.

The attack on the leadership target -- reminiscent of the opening volley of the war on March 19 aimed at Saddam -- occurred in Baghdad's upscale Mansour neighborhood. U.S. officials, speaking on condition of anonymity, said American intelligence learned Monday morning of a high-level meeting in Baghdad between senior Iraqi intelligence officials and, possibly, Saddam and his two sons, Qusai and Odai.

The bombardment left a huge hole where the building had been and reduced three adjoining houses to a heap of concrete, mangled iron rods and furniture.

Military sources told Fox News that in terms of Saddam, "We are certain he went in and we did not see him leave."

U.S. officials told Fox News they were able to learn that those present at the meeting were discussing how to get out of the city and they were standing within 4-6 meters of each other at the time of the strike. The officials said the location is now a huge crater, and that "whoever was in there is dead."

A U.S. Defense official said it would take about three days to verify whether Saddam and his two sons were killed in the blast.

The location hit had a bunker/underground emplacement and is near underground tunnels, which could have facilitated an escape route.

U.S. officials also told Fox News they believe they have come within minutes of getting Saddam in the last two weeks, so much so that he escaped or left locations that minutes later were struck. So there were a number of near misses.

Overall, the presence of U.S. forces in Baghdad has created numerous opportunities to track Saddam.

U.S. officials said they are getting more and more helpful information from the Iraqi people every day, but it is always suspect -- still, this time they acted quickly.

A senior Bush administration official confirmed to Fox News that the U.S. government received time-sensitive information on the ground in Baghdad Monday morning before the new strike against Saddam.

The official said there is a high degree of optimism, but more must be learned -- cautioning that there have been several leadership hits since the decapitation strike that opened the war and this is in keeping with those rapidly targeted attacks.

U.S. officials told Fox News: "If Saddam did not slip out, we believe we will get some confirmation soon by way of physical evidence/human remains at the site and by monitoring communications. ... If he is dead, we believe communications will indicate that."

U.S. officials said Saddam remains very crafty in his ability to evade electronic surveillance, and noted that he was once an intelligence official himself.

The officials said they had a high degree of confidence in the intelligence and expected Saddam and sons to have been there -- but cautioned that they could not confirm they were there for sure. Officials say there was definitely a meeting of a few dozen officials, but Saddam's presence is not confirmed.

Monday was the third straight day the Army penetrated Saddam's seat of power. This time, though, there were plans to stay. Rather than withdrawing at nightfall, as units did over the weekend, members of the 2nd Brigade of the 3rd Infantry Division hunkered down for the night at the sprawling, splendored New Presidential Palace where Saddam once slept.

Several miles away, two soldiers and two journalists were killed in a rocket attack on the 3rd Infantry Division south of Baghdad, the U.S. Central Command reported. Another 15 soldiers were injured in the attack on an infantry position south of the city.

On the other side of town, Marines encountered tough fighting as they entered Baghdad for the first time, coming under machine gun fire. Lt. Col. B.P. McCoy said two Marines were killed and two were injured after an artillery shell hit their armored personnel carrier.

Marines crossed into Baghdad from the east, their engineers deploying a temporary pontoon bridge over a canal at the southern edge of the city after Iraqis rendered the permanent structure unsafe for heavy, armored vehicles.

Hours later, the sound of occasional American artillery split the night air.

The regime, its brutal hold on a country of 24 million slipping away, denied all of it. "There is no presence of American infidels in the city of Baghdad, at all," insisted Iraqi Information Minister Mohammed Saeed al-Sahhaf.

The Iraqi government maintained its hold over state-run television and radio -- arguably its most important remaining levers of control over the country -- and broadcast emotional appeals to resist U.S. forces. Also shown were images of Saddam meeting with key advisers.

The American military flexed its muscle in downtown Baghdad while British officials said one of the regime's most brutal leaders, Ali Hassan al-Majid, had apparently been killed in a weekend airstrike in the southern city of Basra.

A cousin of Saddam, al-Majid was dubbed "Chemical Ali" for ordering a poison gas attack that killed thousands of Kurds in 1988.

Defense officials also said testing was under way on samples taken from a site where soldiers found metal drums possibly containing nerve gas or another type of chemical weapon. A local commander said it was possible the substance was a pesticide, since it was found at an agricultural site near Hindiyah, south of Baghdad.

After a two-week siege, British forces claimed control over Basra, a city of 1.3 million. Hundreds of civilians, women in chadors and barefoot children among them, poured into the street to welcome the invaders. Some handed pink carnations to the British troops in appreciation.

American and British troops advanced in Iraq as their political leaders were meeting in Belfast, Northern Ireland. For President Bush and British Prime Minister Tony Blair, it was the second summit since the fighting began.

"The hostilities phase is coming to a conclusion," Secretary of State Colin Powell told reporters. Without elaboration, he said the U.S. government is sending a team this week to Iraq to begin laying the groundwork for an interim authority.

In the war zone, Americans felt confident enough for Gen. Tommy Franks, overall commander of Operation Iraqi Freedom, to visit troops in Najaf and elsewhere. The four-star general wore camouflaged body armor and a black beret as his Black Hawk helicopter carried him on his tour.

Gen. Richard Myers, chairman of the Joint Chiefs of staff, said all but "a couple of dozen" of the Iraqi military's tanks had been destroyed in less than three weeks of combat.

Senior officials at the Pentagon said the Army assault into Baghdad was part of an attempt to persuade Iraqi forces that further resistance was futile. The military would like to avoid an all-out urban battle in Baghdad, with its 5 million inhabitants.

Missiles screamed overhead and explosions shook buildings inside the city as more than 70 Army tanks, more than 60 Bradley fighting vehicles and an estimated 3,000 troops pushed their way into the heart of Baghdad.

Iraqi snipers fired on soldiers from rooms in the al-Rashid hotel, and tanks returned fire with their main guns and .50-caliber machine guns.

Across the river from the New Presidential Palace, Iraqis took up positions around the University of Baghdad, firing heavy machine guns across the 400-yard width of the Tigris River. Americans responded with mortar fire and close air support to rout the Iraqis.

Fox News' Rita Cosby, Ben Johnson, Carl Cameron, Bret Baier, Ian McCaleb, Major Garrett and The Associated Press contributed to this report.