The planned expansion of the alliance's operation to the rest of the country will consolidate most military responsibilities under the command of top Nato leader, British Lt Gen David Richards.

The overall American force level in the country will remain unchanged, said Mark Laity, an alliance spokesman in Kabul.

Some 8,000 US troops tracking al-Qaeda terrorists or involved in aerial operations will remain under direct US command, Laity said, but the US-led coalition commanded by US Lt Gen Karl Eikenberry will be phased out.

"In a few days, on a date yet to be declared, you will see the completion of the steady expansion of Isaf," the Nato-led International Security Assistance Force, Laity said.

The 12,000 US troops in the regional command in eastern Afghanistan headed by US Army Maj Gen Benjamin Freakley will fall under Nato command.