But US Defense Secretary Donald Rumsfeld warned that tougher fighting lay ahead, including the potential use of chemical weapons against US forces as they move on Baghdad.

"We have been pressuring them on the ground and in the air," Rumsfeld said after meeting with members of Congress.

"My sense is, however, that the Republican Guard that pretty much ringed Baghdad at the present time will probably represent some difficult days ahead and dangerous days ahead in terms of fighting," he said.

The risk Iraqi forces will use chemical weapons has been raised in intelligence "chatter" and by the discovery of caches of chemical protective gear, Rumsfeld said.

"It's hard to believe its stored for any other reason than to protect their people in the event they decide to use those weapons," he said.

Major General Stanley McChrystal, vice director of operations of the Joint Staff, said he did not expect US forces to seize Baghdad in a "coup de main." But he said the fighting "is clearly threatening Baghdad and threatening the core of the regime."

As US forces made dramatic advances on the battlefield, Americans celebrated the commando rescue of a 19-year-old soldier, Private First Class Jessica Lynch, who was captured nine days ago when her supply convoy took a wrong turn in the southern city of Nasiriyah.

"We're just glad to have our daughter back," her father Greg Lynch said.

The US 3rd Infantry Division seized a bridge over the Euphrates river, 30 kilometers (20 miles) south of Baghdad, the last major obstacle to a push on the Iraqi capital, US military sources in the region said. McChrystal said US forces were within 50 kilometers (30 miles) of Baghdad.

The Medina and Baghdad Republican Guard divisions, which were defending the approaches to Baghdad at Karbala and Al Kut, were "no longer credible forces," McChrystal said.

They "cannot maneuver as a division, cannot defend effectively, are not effectively able to counterattack. And that's what we're seeing with a couple of these divisions."

"We are seeing some surrender, but not in tremendous numbers. We are essentially able to move through. It's unclear what is happening to some of those elements," he said.

The general also discounted the possibility that the Republican Guard formations were retreating into the city.

"As we are destroying many of those organizations in place, their equipment in place, as people melt away, it's very difficult to stop very small groups of people. But organized formations would have a very difficult time pulling out," he said.

Remnants of those forces were putting up sporadic resistance, however, and other Republican Guard units and regular army troops have been brought in to reinforce the sectors they were defending, he said.

McChrystal said the Iraqi military still exhibited some control over their forces since they were maneuvering.

"But having said that, there is command and control, but effective command and control, effective maneuvers is not as evident," he said.

Pentagon spokeswoman Victoria Clarke, who has sought throughout the conflict to keep expectations in check, told reporters "we want to underscore again that some of the toughest fighting may well lie ahead."

"They're fighting. We have superior forces, superior capabilities. The end is inevitable. We know how this is going to end. But they are fighting. They're not just sitting there waiting for this to happen to them," she said.

Concurring, McChrystal said, "We are not expecting to drive into Baghdad suddenly and seize it in a coup de main or anything like that."

He said potential use of chemical and biological weapons remained a concern although no such use has been reported so far in the 13-day-old ground war.

"Clearly, as we threaten the core of the regime which Baghdad and Tikrit represent, we believe that the likelihood of them using those weapons goes up. And so, the posture of our force is prepared for that," he said.

He warned, "It'll be a grave mistake for either who orders it or the people who execute it; but it also won't change the outcome on the ground. We'll still be able to maneuver, we'll still be able to execute the operations as planned."

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