Heavy fighting has left scores of casualties in eastern Afghanistan, where U.S. and Afghan-led coalition forces are battling al-Qaida and Taleban fighters.
Defense Secretary Donald Rumsfeld says nine Americans have died so far in the offensive, the biggest of the five-month-old war.
A senior U.S. official tells reporters seven lost their lives when an MH-47 Special Operations helicopter came under small arms fire and crashed. An eighth soldier was killed in a separate incident in which another helicopter came under fire. The ninth was reported killed in a mortar attack.
At least 40 Americans have been wounded.
But Defense Secretary Rumsfeld says al-Qaida and Taleban losses have been much heavier. "The enemy forces have sustained much larger numbers of killed and wounded, and there will be many more. We intend to continue the operation until those al-Qaida and Taleban who remain either surrender or are killed. The choice is theirs," he said.
Defense officials say hundreds of al-Qaida and Taleban are entrenched in caves and other well-defended positions in mountainous terrain south of Gardez in eastern Afghanistan. The build-up of hostile forces had been monitored for some time before the assault began late Friday.
More than 1,000 U.S. troops are involved along with allied Afghan forces and troops from Australia, Canada, Denmark, France, Germany, and Norway.
They are receiving air support from a variety of fighters, bombers, and other attack aircraft. The Pentagon says more than 350 bombs have been dropped.
Mr. Rumsfeld says coalition forces will continue to increase the pressure on the al-Qaida and Taleban who have been encircled in the operation to prevent escape.
But Mr. Rumsfeld rejects suggestions that this may be the last stand of hostile forces in Afghanistan. He says there are undoubtedly other pockets of resistance and predicts further major battles.