THE US Army's 3rd Infantry Division dashed north today toward the Shiite holy city of Karbala, only 50 miles south of Baghdad, but was stalled by a sandstorm that blew out of the desert in the afternoon.

THE US Army's 3rd Infantry Division dashed north today toward the Shiite holy city of Karbala, only 50 miles south of Baghdad, but was stalled by a sandstorm that blew out of the desert in the afternoon.

Allied planes were due to fly more than 1,000 sorties today - 800 of them in the Baghdad area where elite Republican Guards were to be targeted.

To the south, British troops and Iraqi forces exchanged artillery fire on the outskirts of Basra, Iraq's second largest city.

Troops from the British 7th Armoured Brigade were south and west of Basra, as irregular units - the elite Republican Guard, Special Security Organisation forces or the paramilitary militia Fedayeen - kept coalition forces from taking the city, British officials said.

A US official said British forces outside Basra were under heavy fire.

"This is not a video game where everything is clear and neat and tidy. Some enemy who feel that they want to carry on fighting will inevitably do so," said Lieutenant Colonel Ronnie McCourt, a spokesman for British forces in the Gulf, speaking at US Central Command in Qatar.

US troops made rapid advance toward Baghdad under heavy allied air protection that wiped out a column of charging Iraqi armour and sent some of Iraqi leader Saddam Hussein's outer defences withdrawing toward the city. But weather halted the long columns of thousands of vehicles that stretched across the desert and farmlands.

The trip north passed bombed anti-aircraft guns, empty foxholes and berms dug for tanks that had been abandoned by Iraqi forces.

Outside the Shiite holy city of An-Najaf, south of Karbala, US soldiers skirmished with Iraqi forces before dawn. Iraqis shot rockets and anti-aircraft guns at the Americans.

Small groups using pick-up trucks or on foot tried to approach US positions but were driven back by tank and artillery fire.

Mosques in the cities of An-Najaf and Karbala are the most sacred sites to Iraq's majority Shiite Muslims after those in Saudi Arabia.

An-Najaf is the site of the tomb of Imam Ali, the son-in-law and cousin of Islam's Prophet Muhammad. Shiites aspire to bury their dead in its cemetery, which stretches for miles and is the largest in the Muslim world.

To the south-east near An Nasiriyah, US Marines continued to cross the Euphrates River and a convoy of hundreds of vehicles - including tanks, TOW missiles and armoured personnel carriers - was backed up along the road leading to a pontoon bridge.

Two bloody battles Sunday near An Nasiriyah, 230 miles from Baghdad, left nine Marines dead and a dozen US soldiers missing and presumed captured.

In one incident, a group of Iraqis waved a white flag in surrender, then opened up with artillery fire. Another group appeared to welcome coalition troops, then attacked them, US officials said.

Navy jets from the carrier Harry S Truman in the Mediterranean Sea dropped bombs and fired laser-guided missiles at sites in northern Iraq where weapons of mass destruction were suspected of being produced, navy officials said.

Aircraft from Mediterranean-based carriers for the first time flew over Turkey on their way to strike targets inside Iraq, said battle group commander, Rear Admiral John Stufflebeem.

Also, US Marine officials revealed today that US forces had been in northern Iraq for nearly 24 hours.