Hundreds of US Marines and Afghan special forces on Saturday trekked far into remote Afghan mountains to retake a valley controlled by militants suspected of ambushing a team of US commandos and shooting down a special forces helicopter.
The major offensive in eastern Kunar Province, near the border with Pakistan, is the biggest yet against those believed responsible for the twin attacks on June 28, the deadliest blow for US forces in Afghanistan since ousting the Taliban in 2001.
Three members of a four-man Navy SEAL team were killed in the ambush, and all 16 troops on board the Chinook chopper that was sent to rescue them died when it was hit by a rocket-propelled grenade.
Saturday's offensive came after a deadly week for US forces in Afghanistan. Seven American troops have died, as well as dozens of suspected militants and civilians, reinforcing concerns that crucial elections next month to choose lawmakers for a new legislature may be threatened by widespread violence.
Hundreds of Afghan rebels, as well as militants from Pakistan, Saudi Arabia and Chechnya, are thought to be hiding in Kunar's Korengal Valley and are intent on disrupting the elections, according to US military and Afghan special forces commanders in the area.
"We want them running for their lives way up in the hills where they can't attack polling stations," said Captain John Moshane, of the 2nd Battalion, 3rd Marine Regiment, based in Hawaii. "We want to isolate them from the community."
US and Afghan forces started moving into position at one end of the valley on Thursday, about 190km east of the capital Kabul. They were digging mortar and machine-gun pits for a temporary resupply base in the middle of a corn field near Kandagal, a village of about 100 farmers and their families.
The move sparked an immediate response from the militants, who attacked a nearby US base and a convoy of troops with rockets, but they all missed.
US and Afghan troops started hiking into the rugged mountains on Friday and Saturday, as A-10 attack aircraft circled high above. Many of the teams led lines of donkeys laden with food and water. The operation was expected to last at least two weeks, Moshane said.