Troops from Iraq's elite Republican Guard are moving in a huge column of around 1,000 military vehicles from Baghdad to Najaf, CNN quoted US Army officers as saying on Wednesday night [India time].

They are travelling towards the lead elements of the US Army's 3rd Infantry Division, the channel said.

Coalition military officials expect them to try and retake a key bridge on the Euphrates River, CNN said.

US commanders are trying to call in air support, but coalition helicopters and planes are not able to take off due to a sandstorm in the region, it said.

In the Kurdish-controlled northern part of Iraq, around 1,000 troops from the US Army's 173rd Airborne Brigade have taken control of a key airfield, CNN quoted an American official as saying on Thursday morning.

British warplanes are attacking a convoy of 70 to 120 Iraqi armoured vehicles that is heading southeast from Basra towards the al-Faw peninsula, BBC reported.

At the Pentagon, CNN quoted an official as saying that the coalition may have miscalculated the capability of Iraqi paramilitary fighters.

"We may have underestimated that they were dispersed to so many places across Iraq to enforce regime discipline," he said. "It's clear now they dispersed sometime before the war began."

But President George W Bush said that the coalition's victory is certain.

"As they approach Baghdad, our fighting units are facing the most desperate elements of a doomed regime," he told troops at the MacDill Air Force Base in Florida.

"We will stay on the path, mile by mile, all the way to Baghdad and all the way to victory," Bush said

Earlier, an American missile strike hit a busy Baghdad market, killing 15 people and incensing the residents.

Three apartment blocks located on the shopping street in the Al-Shaad district of the Iraqi capital were destroyed in the attack.