British soldiers will join other Nato troops in southern Afghanistan

Lt Col Henry Worsley gave the warning as 3,300 troops prepared to go to the southern Afghan province of Helmand.

While they are not expected to deal with the illegal heroin trade and poppy farmers, they could be targeted by Taleban "bomb making cells", he said.

UK troops will join about 9,200 Nato-led multi-national forces.

Lt Col Worsley told BBC's defence correspondent Paul Wood that he expected a rise in Taleban attacks in the short term.

If I was a Taleban commander I would - seeing all these extra troops suddenly in the area - I'd want to assert my authority Lt Col Henry Worsley

"I think there's bound to be an increase from the Taleban.

"If I was a Taleban commander I would - seeing all these extra troops suddenly in the area - I'd want to assert my authority.

"But there's a formidable force coming in here and I'm quite certain that the robust approach that they'll have will stop that pretty quickly."

Defence Secretary John Reid has said British troops were going to help with civilian aid and economic development, and to help Afghan President Hamid Karzai to reconstruct the country.

The extra UK troops will join the 1,100 already in the country and 1,950 announced earlier, but the total at any time is not expected to exceed 5,700.

The Nato force - the International Security Assistance Force - replaces an existing and smaller US force.