President Donald Trump Monday left the door open to a possible political agreement with the Taliban, in an address to the nation on America's strategy in the 16-year Afghan conflict.

"Some day, after an effective military effort, perhaps it will be possible to have a political sentiment that includes elements of the Taliban in Afghanistan," he said.

"But nobody knows if or when that will ever happen," he added, before vowing that "America will continue its support for the Afghan government and military as they confront the Taliban in the field."