A Marine battalion overran a Republican Guard headquarters and seized one of Saddam Hussein's palaces south of the city. Overhead, U.S. warplanes were flying around the clock, coordinating precision strikes in support of upcoming ground attacks.
The new round of attacks came after Saturday's 25-mile incursion through an industrial section of southern Baghdad in which up to 3,000 Iraqi fighters were killed.
In addition to the fighting on the southern edges of the city, coalition troops were "preventing enemy movement in and out of the city in certain places around the city," said Capt. Frank Thorp, a U.S. Central Command spokesman at Camp As Sayliyah in Qatar.
"Baghdad is being isolated," he said.
U.S. forces have troops stationed around three-quarters of Baghdad's perimeter: the 3rd Infantry Division along the south and southwest edges of the city; 1st Division Marines on both sides of the Tigris to the southeast; and — according to a U.S. military official speaking on condition of anonymity — at key points just to the north and northwest. That leaves only the northeast arc around Baghdad free of American forces.
In other major developments:
While Saturday's show-of-force foray into Baghdad by American armored vehicles was brief, it inflicted a heavy toll, according to U.S. Central Command spokesman Jim Wilkinson. More than three-dozen tanks and armored vehicles were involved; U.S. casualties were described as light.
The blitz took two task forces of the 3rd Infantry Division from the southern outskirts of the city past Baghdad University and near the banks of the Tigris River, then back to the western outskirts of the city to the airport, which is under U.S. control.
Capitalizing on their dominance of the skies, U.S. commanders began deploying planes over Baghdad 24 hours a day, ready to direct strike aircraft to ground targets. The sound of explosions, artillery and the scream of rockets resounded in Baghdad for most of the morning Sunday.
U.S. officials made clear that forays into Baghdad would continue. Television footage showed a second raid Sunday.
"It's important to do so to secure the area; it's also important that we do that for psychological reasons," Wilkinson said. "Frankly we've had to prove to the civilians in the north and the south that we're there to stay. Once they know we're there to stay, they celebrate."
In southern Iraq, British forces staged their largest military incursion yet into the city of Basra on Sunday, with a column of 40 armored personnel carriers rumbling into the city.
Group Capt. Al Lockwood, spokesman for British forces in the Persian Gulf, said that for the first time troops have set up checkpoints in Basra, where British forces and Iraqi paramilitaries have waged bloody battles for control of the key southern city. The British forces have been reluctant to stage a direct attack on the town of 1.3 million.
"We are aggressively patrolling, we're moving into the city now," Lockwood said, adding that troops believe they have weakened the Iraqi paramilitary resistance to such an extent that a British presence can be established inside the city limits.