Gates: Some U.S. troops could leave Afghanistan this year

The outgoing U.S. defense chief applauded the effort to recruit and train strong Afghan police, security and military forces, according to a transcript of the media briefing provided by the Pentagon. Overall, he is "cautiously optimistic" about the U.S.-led mission there.

“I do feel like the pieces are coming together,” Gates told reporters, adding a warning: “The gains are fragile and reversible.”

The annual spring fighting season is about to kick off there, a time Gates said will be “an acid test” of “how effective the progress that we've made is going to be.”

Gates said Washington’s announcement that some U.S. forces would be removed from Afghanistan this summer got the attention of both Afghan officials and the population there.

That announcement, and a subsequent one that thousands of U.S. forces would stay until 2014, spurred growth of indigenous security and police forces.

The 2014 announcement led Afghan officials to “believe that we are going to be around for the longer haul.”

Gates’ comments made clear any removal of a small number of U.S. troops this year would be highly nuanced. He said it would be a “gradual process” based on “conditions on the ground.”