British spokesmen said their forces were intent on seizing more territory as a show of force for local residents and militias in Iraq's southern city, which has been encircled by British-American troops for about two weeks.

Group Captain Al Lockwood, a British spokesman at the war headquarters of the US Central Command in Qatar, told the BBC that several armored brigades had moved forward.

"Our initial objective is to take some of the outskirts of Basra, set up vehicle checkpoints ... and to take some ground," Lockwood said. A British television reporter at the scene said hundreds of tanks were involved.

The advance, Lockwood later told CNN, was intended "to reassure the people of Basra that we are there, to show the para-militaries that we are there and that we are controlling the area that we are now in."

Earlier, British military spokesman Chris Vernon said in Kuwait that the decision to send in the tanks was made after battle planners estimated that the Iraqi's "defences have been weakening."

"So the forward battlegroup commander and the brigade commander, as entirely in line with the way we operate, made the decision this morning, here's the opportunity, the conditions are right, let's go for it," Vernon told Sky News.

"Constantly we've been eroding on the outskirts.

"We've been targeting the Baath party officials and the irregulars very, very successfully and we had a very big hit the other day on some very senior officials," he said.

The so-called Desert Rats, from Britain's 7th Armoured Brigade met "patchy" resistance as the troops moved in from the southwest, an unnamed military source told the Press Association, Britain's domestic news agency.

The source, at Central Command in Qatar, said there was some "stiff fighting" early Sunday morning in the city, with a population of some 1.5 million people.

In London, a spokeswoman for the British defence ministry declined to comment on the reports.

But she said the war was not a conventional conflict with a front line, and that units could enter the city and withdraw as they pleased.

A reporter with Britain's ITV News, Juliet Bremner, who was with the rolling convoy heading into Basra, said hundreds of tanks were travelling down one of the main highways which leads directly into the north of the city.

"As far as we know there shouldn't be too much of a problem getting into Basra itself. There seems to be nothing to stop them," she said.

"No rocket propelled grenades have been fired at the convoy so it should be a pretty straight-forward route into the city. There are no signs of firing or any signs of resistance," she added.

SPACE.WIRE