British forces set up a Checkpoint at a bridge outside Basra on Sunday. Reuters quoted Witnesses as saying that the British troops in 8-10 armoured vehicles had set up the checkpoint at the Zubair bridge south of the city and were checking cars heading into Basra. Britain withdrew its forces from Basra in December and a remaining contingent of 4,100 troops has largely kept to a base outside the city during the past six days, in which government troops have battled militia forces. "We've had ground forces outside the wire assisting Iraqi forces. There are no British ground forces inside the city of Basra," spokesman Major Tom Holloway said by telephone. "As yet there is no intent to push British armour into the city." The U.S. military has confirmed that it has special forces operating alongside Iraqi troops in what began as an Iraqi-led operation. They have called in air strikes from U.S. warplanes. Holloway said British forces have also fired artillery in support of British ground forces.