The expected major confrontation between US-led coalition forces and Iraqi troops drew closer late last night as a contingent of the Republican Guard headed south from Baghdad in a 1,000-vehicle convoy, under cover of a sandstorm, toward US Marines in central Iraq.
A column of 120 Iraqi armoured vehicles was reported to be engaging with British forces in a separate confrontation at Basra.
About 1,000 US troops have parachuted into northern Iraq and seized an airfield in Kurdish-controlled territory, US military said. The troops from the 173rd airborne brigade seized the airfield to clear the way for armoured tanks and Bradley fighting vehicles - a precursor to establishing a second front.
Meanwhile, there were reports last night that President Bush will ask the British Prime Minister, Mr Tony Blair, for the commitment of at least 4,000 more British troops when they hold their war summit later today. They had a working dinner last night.
Mr Bush has announced the US is to fly its elite 4th Infantry Division and other units totalling more than 30,000 troops to the Gulf within days.
Before flying to Washington the Prime Minister told the Commons the current assessment was that they had sufficient troops already in the Gulf.
After leaving Britain Mr Blair also gave a clear signal he did not anticipate the swift emergence of an Anglo-American blueprint detailing the possible or likely role of the UN in the government of a post-Saddam Iraq.
Having told MPs he believed a UN resolution for a replacement government was necessary, Mr Blair also insisted the arrangements for the interim administration of Iraq in an immediate post-conflict situation must provide for the protection of allied forces who remained there.
Coalition strategy in the conflict suffered a setback as the US-led forces admitted they had launched a missile attack on a residential area of Baghdad because Iraqi munitions were stored there. The admission came after reports that 15 civilians were killed when cruise missiles hit a heavily-populated area of the city early yesterday.
In a statement last night following the Baghdad incident, US Central Command in Qatar said "civilian damage" was possible as a result of the attack in which precision-guided missiles targeted nine Iraqi surface-to-surface missiles and launchers.
The statement added: "The missiles and launchers were placed within a civilian residential area. Most of the missiles were positioned less than 300 feet from homes. A full assessment of the operation is ongoing."
But the statement added such targets were a threat to Coalition forces and would continue to be attacked: "While the Coalition goes to great lengths to avoid injury to civilians and damage to civilian facilities, in some cases such damage is unavoidable when the regime places military weapons near civilian areas."
Reacting to the news and to reports of Iraqi forces putting civilians at risk, the UN Secretary General, Mr Kofi Annan, said he was "getting increasingly concerned by humanitarian casualties in this conflict."
He added: "I would want to remind all belligerents that they should respect international humanitarian law and take all necessary steps to protect civilians."
In Basra, British forces fought with Iraqis for control of Iraq's second city. Previous reports of a citizens' uprising against the Saddam Hussein regime remained unconfirmed. The city's electricity supply came to a halt last Friday during US-British bombing raids. As a result, the city's water supply and treatment system was shut down.
News of the major Iraqi advance southwards from Baghdad came as some US units in central Iraq appeared to be adjusting their strategy to deal with attacks from Iraqi paramilitaries.
Instead of hastening towards Baghdad, these units were moving slower to clear out pockets of opposition.