THE ground campaign for Baghdad has intensified as US forces clashed with Iraq's Republican Guard near Karbala, 50 miles southwest of the capital.

This was the the first major ground assault against the troops charged with defending Baghdad and as of late Tuesday evening, the Pentagon had not released a casualty report.

The 3rd Infantry, moving north along the Euphrates River, engaged one of the Republican Guards' top units, the Medina Division, which had been positioned to defend the southern approach to Baghdad.

Air Force Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said the Medina Division has been weakened by massive bombing raids to less than 50 percent capability.

The Medina Division distinguished itself as one of Iraq's fiercest units in 1986 defending the southern port city of Basra from Iranian forces after they invaded the Al Faw peninsula.

The hope is that Iraq's Medina Division can be weakened before it can retreat to Baghdad where coalition forces potentially face a brutal urban battle that could drag on for weeks.

Coalition forces may also have to take on the Republican Guard's elite Nebuchadnezzar and Hammarabi divisions before entering Baghdad. Some of the half dozen Republican Guard divisions were being moved this week in preparation for a coalition assault on Baghdad.

Before the ground fighting began near Karbala, Defense Secretary Donald Rumsfeld said "the circle is closing" around Baghdad.

Earlier on Tuesday, U.S. warplanes bombed Baghdad and its southern suburbs.

"These attacks were intended to create vulnerabilities in the Republican Guard defenses, and also to isolate the remaining pockets of resistance for destruction at a time of our choosing,'' Army Brig. Gen. Vincent Brooks told reporters in Doha, Qatar.