U.S. Defense Secretary Robert Gates has called for the U.S. military to keep up the pressure on the Taliban in Afghanistan.

Gates said he doesn't believe the Taliban will engage in serious talks about ending their fight until they are under extreme military pressure.

He acknowledged that "there's been outreach" to the Taliban by the U.S. and other countries, but he describes the contacts as "very preliminary at this point."

Afghan President Hamid Karzai said Saturday that the U.S. and Afghan government have held talks with Taliban emissaries in an effort to end the nearly 10-year old war.

"My own view is that real reconciliation talks are not likely to be able to make any substantive headway until at least this winter," said Gates, who retires as defense secretary at the end of the month.

"I think that the Taliban have to feel themselves under military pressure, and begin to believe that they can't win before they're willing to have a serious conversation," he told CNN's "State of the Union" in an interview taped Saturday after Karzai's announcement.