The deployment on Wednesday came hours after Iraq's most feared group released a video threatening to behead a Japanese captive within 48 hours unless Japan withdraws its troops from Iraq.
The British troops, headquartered in Basra, are heading to an area near the capital to replace US troops who are expected to launch a major offensive in areas west and north of the capital.
"We can confirm that there is some movement," said British military spokesman Major Charlie Mayo. He gave no specifics on troop numbers, citing security concerns.
British soldiers' families are
worried over the move
Large flatbed trucks were seen carrying armoured British vehicles up a road through Iraq's southern desert to Nasiriya, 320km southeast of Baghdad where it appeared the troops were stopping for the night.
At least five convoys of tanks, towed on lorries, Land Rovers and other army vehicles were on the road, accompanied by US Humvees.
Helicopters were seen buzzing above the convoys as they rumbled northwards, headed for Babil province, just south of the Iraqi capital, packed with soldiers.
Nearly 800 Scottish soldiers of the First Battalion Black Watch are expected to be based in an area just south of Baghdad to free up American forces for an expected assault on Falluja and other areas.
The move is part of an effort to bring order to Iraq before elections in January.
"They're going to get one hell of a kicking this time"
father of two Black Watch troops
British officials have been vague on the precise destination, with some media reports indicating the Black Watch would be sent to Iskandariya, north of Hilla.
The British soldiers' families expressed worries on Wednesday that the redeployment puts the troops in greater danger.
"It wasn't a cake walk in Basra but it's going to be a lot, lot more dangerous up there," said James Buchanan, 56, from Arbroath in central Scotland, who has two sons with the regiment in Iraq. "They're going to get one hell of a kicking this time," he said.
In London, British Prime Minister Tony Blair on Wednesday pledged that a battle group on a US-requested mission near Baghdad would be home by Christmas, but left open the possibility that other British troops may have to replace them.
Blair said the Black Watch troops
would return home by Christmas
"The Black Watch will come back by Christmas. As to what then happens, we can't be sure at the moment," Blair said.
"We don't believe that there will be a further requirement for our troops but I can't commit myself, I can't guarantee that," he told parliament.
Blair said Washington had made no commitment that it would take over from the British battalion in December.
"I haven't been given such an assurance, I haven't sought that sort of assurance," he said.
But the prime minister said London was committed alongside Washington to a joint mission to help stabilise Iraq.
"We're engaged in a joint operation in Iraq ... to make sure elections in Iraq can take place in January," he said, adding that that he "passionately believed [the joint effort] is in the interest of this country".