US Marines and Afghan troops have launched an offensive to take a remote mountain valley from insurgents tied to the deadliest blow on American forces since the Taliban regime was ousted nearly four years ago.
The operation is the biggest yet aimed at rebels believed responsible for twin attacks that killed 19 US troops in June. Three Navy SEALs were killed in an ambush, and all 16 soldiers on a helicopter sent to rescue them died when it was hit by a rocket-propelled grenade.
The offensive came at the end of a deadly week for US forces in Afghanistan.
Seven Americans have died along with dozens of militants and civilians, reinforcing concerns that crucial legislative elections next month could be threatened by a surge in violence.
US and Afghan commanders said militants in the Korengal Valley, in eastern Kunar province near the Pakistani border, were intent on disrupting voting.
They said the valley held hundreds of Afghan rebels, as well as extremists from Pakistan, Saudi Arabia and Chechnya.
Hundreds of Marines and Afghan special forces troopers started moving into position at one end of the valley Thursday, about 120 miles east of the capital, Kabul. They dug mortar and machine-gun pits for a resupply base in a corn field near Kandagal, a village of about 100 farm families.
Reacting quickly, rebels fired rockets at a nearby US post and a troop convoy but did not hit anything.
American and Afghan forces hiked into the rugged mountains Friday and Saturday, many leading lines of donkeys laden with food and water. A-10 attack planes circled high above.
The operation was expected to last at least two weeks.