"It started at first light," said Colonel Will Grimsley, commander of the First Brigade of the US army's 3rd Infantry Division.

Grimsley said elements of the division's Second Brigade had come under rifle fire and attack by rocket-propelled grenades (RPGs) as they entered the heart of Baghdad. He did not give the size of the US force advancing.

He was speaking at Baghdad airport a day after US forces seized control of most of the facility in their 16-day-old drive northward to topple Saddam's regime.

CNN earlier reported that US armour had penetrated the "heart of Baghdad" early Saturday encountering occasionally stiff resistance from Iraqi forces using RPGs and horizontally fired anti-aircraft weapons.

SPACE.WIRE