General John Nicholson said the aim was to drive back the Taliban to less than 10 percent of the population, an ambitious goal considering the militants are estimated to control or contest about 40 percent of the country.

"This, we believe, is the critical mass necessary to drive the enemy to irrelevance, meaning they're living in these remote outlying areas, or they reconcile, or they die," Nicholson told a Pentagon news briefing via video conference from Kabul on November 20.

Nicholson said the goal, if achieved, would give the Kabul government greater legitimacy and would ensure credible general elections in 2018 and a presidential vote in 2019.

Since announcing his new Afghan strategy in August, U.S. President Donald Trump has sent an additional 3,000 troops to Afghanistan, bringing the total number of U.S. troops to about 14,000.

With reporting by Reuters