Canadian Prime Minister Stephen Harper said western forces alone can never defeat the Taliban insurgency in Afghanistan.

Harper also said the United States must come up with a viable exit strategy before asking other countries to do more in the future.

"We're not going to win this war just by staying," Harper said in an interview that aired on CNN on Sunday. "Quite frankly, we are not going to ever defeat the insurgency. Afghanistan has probably had — my reading of Afghanistan history is that's it's probably had an insurgency forever of some kind."

"What has to happen in Afghanistan is we have to have an Afghan government that is capable of managing that insurgency."

The Obama administration is reviewing the war strategy in Afghanistan. Obama recently announced that 17,000 additional U.S. troops would deploy to Afghanistan this year.

Obama declined to ask war-weary Canada to extend its mission in Afghanistan when he visited Canada last month.

Canada, which has lost more than 100 personnel in Afghanistan, is withdrawing its 2,500 combat forces out of the volatile south in 2011.

"Over the long haul, if President Obama wants anybody to do more, I would ask very hard questions about what is your strategy for success and for an eventual departure," Harper said.

The comments are not a radical departure from Harper's past observations but he has rarely been so blunt in assessing the situation.

Canadian and other NATO troops have made some gains against the insurgents over the years but those gains are not irreversible and the overall success has been "modest," Harper said.

Western forces cannot indefinitely ensure the security of the country, nor can outsiders hope to govern Afghanistan.

"Ultimately, the source of authority in Afghanistan has to be perceived as being indigenous. If it's perceived as being foreign, it will always have a significant degree of opposition," Harper said.

The interview was recorded a week ago as Harper visited New York City.

Harper also acknowledged the country is not going to become a western-style democracy "any time soon." But he expressed hope the Kabul government can at least achieve "some democratic rule-of-law norm."