NATO's top commander says the global financial crisis could force U.S. allies to scale back their efforts in Afghanistan, or possibly even pull out.

Supreme Allied Commander Gen. John Craddock said Friday that at least two nations — Canada and the Netherlands — already have signaled they will leave by 2011.

That means the U.S. and other allies will have to cover the costs of securing Afghanistan, which the incoming Obama administration has called a top priority.

Speaking with reporters, Craddock said NATO nations already were stretched thin before the financial meltdown hit last year.

Now, he said, nations will be "challenged even more greatly."