Army Major Ross Coffman said soldiers of the 3rd Infantry Division had completed the western portion of a planned encirclement of Baghdad and were waiting for US Marines to close the door from the east.

In Iraq's second city of Basra, British tanks and infantry seized the "vast majority" of the strategic port after a 10-day siege, an officer said. Witnesses saw British tanks around the ruling Baath Party headquarters.

Troops of the US 101st Airborne Division were meanwhile locked in fierce house-to-house fighting for control of the holy city of Karbala, 80 kilometers (50 miles) southwest of Baghdad, with one US soldier dead and eight wounded.

US forces were intent on surrounding Baghdad a day after launching a tank raid into the capital that met with sporadic but fierce resistance. US officials claimed more than 2,000 Iraqis had died in the battle for Baghdad.

Coalition aircraft flew round-the-clock sorties over Baghdad while mortar and rocket fire was heard downtown for the first time in the war, AFP reporters said.

Major Rod Legowski said the Third Brigade of the US Army's 3rd Infantry Division circled Baghdad northwards from the west Sunday while the marines pushed toward the city from east of the Tigris river.

"We think by the end of today, it (Baghdad) will be totally surrounded," said Legowski, a marine liaison officer with the division.

Coffman said the army troops backed by close air support destroyed an Iraqi tank battalion, leaving hundreds of Iraqis dead or wounded and wiping out 25 tanks, 50 trucks and several armoured personnel carriers.

After completing a 70-kilometer push, the army controlled a semi-circle around Baghdad extending from the Tigris in the north to where the river leaves the capital in the south, the major said.

"The army owns from river to river on the west side," said Coffman, who serves at the division's Tactical Command Post.

News of the maneuver came as US forces consolidated their hold on the international airport southwest of the city and began 24-hour air patrols to support ground troops in an expected major push on the capital.

US Central Command later said a US C-130 military transport plane staged the first coalition landing at the Saddam International Airport.

In a new development, US officers said Egyptians, Jordanians, Saudis and Syrians were now fighting alongside Iraqi troops against US forces moving on Baghdad. "It's a whole conglomerate of Islamic freedom fighters," one officer said.

Cleaning-up operations continued at the airport 20 kilometers (12 miles) outside Baghdad. US commanders said they controlled 95 percent of the facility, with some 5,000 troops in place.

But so-called "friendly fire" incidents continued to plague the US offensive as 18 Kurds were killed and 45 others wounded near the northern city of Arbil when US aircraft mistakenly bombed a convoy, according to Kurdish sources, who denied reports four US special forces troops were among the dead.

Kurdistan Democratic Party (KDP) external relations official Hoshyar Zebari told AFP that all those killed in the friendly fire attack, who included a translator for the BBC, were peshmerga fighters.

Zebari said the dead included many of the commanders of Kurdish forces who are battling, with assistance from elite American units, forces loyal to Saddam on the northern front.

Among the seriously wounded in the attack at Dibaga, 20 kilometresmiles) south of Arbil, was Wajih Barzani, 33, the head of KDP special forces and brother of party leader Massoud Barzani.

The US Central Command admitted that "coalition aircraft may have engaged special operations and friendly Kurdish ground forces approximately 30 miles (50 kilometres) southeast of Mosul".

It later confirmed only that "early casualty reports indicate one civilian may have been killed, (and) one US soldier, one Kurdish soldier and four civilians were injured" and that an investigation was ongoing.

Hospital sources in Arbil said four Americans were among the dead. BBC correspondent John Simpson, who was travelling with the convoy and suffered minor injuries in the attack, also said he saw American dead.

If the details of the attack are confirmed it would be the worst "friendly fire" incident in the 18-day-old US-British war on Iraq.

The Central Command also said three US servicemen were killed and five were hurt in a possible friendly fire clash involving an F-15E Strike Eagle aircraft and coalition ground forces. It provided no further details.

Kurdish fighters and US special forces, supported by targeted air strikes, have been advancing towards the cities of Mosul and Kirkuk after engaging Iraqi forces in the first battles in the region.

In the southern port of Basra, British spokesmen said their forces had siezed all but the old quarter after armoured brigades thrust deep into the city from the south, the center and north.

"We control the vast majority of the city," Vernon said. "But there are some places we don't control, for example the old city." He said to put tanks in the old city would be "very fragile."

A British spokesman later said a British soldier was killed in the push.

The raid came after an air strike against the home of Ali Hassan al-Majid, Saddam's notorious cousin and aide known as "Chemical Ali", who was believed to be organising the defence of the city.

SPACE.WIRE