More than 1,300 U.S. Marines are now based at an airbase southwest of the Taliban stronghold of Kandahar. The forces are already patrolling the area, hoping to cutoff any attempt by Taliban fighters to escape from the besieged city.

Aided by heavy U.S. airstrikes, anti-Taliban tribesmen pressed toward the Taliban's last remaining stronghold of Kandahar on Friday, as American officials warned of potential violence against forces in the region.