NATO's top commander in Afghanistan told senators on Thursday a defeat in the military mission here would be a 'huge blow' to Europe and the United States and would not be allowed to happen.
International Security Assistance Force commander General David Richards also apologised to the upper house of parliament for mounting civilian casualties in the fight against Taliban insurgents.
"If we were defeated then of course it would be a huge blow to Europe, to America and most of the free world," Richards said, under questioning front senators about a failure to curb the insurgency, which has peaked this year.
Richards said NATO understood the importance of its mission and could not fail. "I am absolutely determined that Afghanistan will remain a free and an increasingly prosperous nation," he said.
The British general asked for the support of Afghan elders and parliamentarians to win the war, which has this year claimed more than 3,700 victims, most of them of rebels.
"We will not be defeated because we understand the importance of it. I can assure you there is no chance of it as long as you continue to give us your support," he said.
There are more that 31,000 NATO troops in Afghanistan fighting alongside around 8,000 US-led coalition troops, as well as Afghan army and police. They are facing an insurgency that has grown every year since it was launched after the Taliban were toppled from government by the coalition in 2001.
About 1,000 of this year's dead were civilians, according to Human Rights Watch.
NATO forces have fought especially fierce battles in the southern provinces of Helmand and Kandahar, the birthplace of the extremist Taliban movement that took power in 1996.
The force has been criticised for its heavy use of air power, with allegations that bombings against Taliban caused around 80 civilian casualties on October 24.
ISAF has not released results of an inquiry into the allegations but The New York Times this week cited an unidentified NATO official admitting 31 civilians were killed.
Richards apologised for all civilian casualties, but said the Taliban were also to blame as they sometimes hid in civilian houses.
"We do have a problem. The people who are trying to impose a different way of life on this country hide and fight from amongst your people," he said, adding "when the bullets start flying -- to distinguish between the good and the bad ... is difficult."
Asked about foreign troops raiding homes without consulting local authorities -- an invasion which has sparked much criticism, Richards said his forces were taught about Afghan sensitivities about searching homes.
"Normally when we do a planned operation the Afghan authorities are fully informed but the problem comes when something happens in a hurry and our soldiers want to take advantage of a fleeting opportunity," he said.
The commander said the fledgling Afghan army had come along to the extent it could conduct operations with foreign troops.
"This is very, very important to me because our route out of your country and to giving you enduring success is through developing your military, your police and our interactions with your government," he said.