<p>US ground forces punched through a crucial pathway known as the Karbala Gap at dawn today and surrounded the city of Karbala, advancing toward a much-anticipated assault on Baghdad. The movement occurred after elements of the US Army's Third Infantry Division unleashed an assault on key Iraqi Republican Guard divisions. The attack signaled a new phase in the war: engaging Iraqi tank divisions in ground fighting within a defensive perimeter less than 50 miles from the capital.</p>