"Forcing the crusader forces out of the country has been one of the most important goals of the Taliban in the past six years since they've invaded our territory," Ahmadi said.
There are about 39,000 mostly Western soldiers in Afghanistan under Nato command and about 15,000 in a separate US-led coalition.
Karzai made a new offer of talks with the Taliban on September 9.
He has regularly offered negotiations with the Taliban.
The Taliban was in government between 1996 and 2001, and there have been rumours that contact has already been made by the Afghan authorities with the movement for planned talks.
The Taliban was driven out of government in 2001 after US-led troops invaded the country in the wake of the September 11 attacks on the United States.