US military has started building new facilities in Afghanistan for 20,000 extra troops that will pour into the country early next year.

"There's a very huge building campaign that has already begun. We're pushing dirt as we speak for the arrival of these forces," Maj. Gen. Michael Tucker, deputy commander for operations for US forces in Afghanistan said on Friday.

Tucker told the reporters that the plan was to house the 20,000 extra troops, who would be joining the 32,000 American forces already there. The top commander refused to say where the new facility would be, he only provided few details.

"We have done in depth studies on specifically to the man how many building spaces, how many helicopter pads...how many latrines, how many dining facilities...down to the actual number of boots on the ground."

The planned injection of extra US forces is a policy that Barack Obama has said he will also pursue when he takes office.

US defense officials have asked for four more combat brigades, along with thousands of other support forces, including intelligence and surveillance personnel.

One of the brigades is expected to arrive in Afghanistan in January.

RZS/HAR