The Senlis Council report claimed that 54 percent of the country is under Taliban control.

The Taliban is gaining a "significant amount of psychological control, gaining more and more political legitimacy in the minds of the Afghan people, who have a long history of shifting alliances and regime change," said Senlis, whose report was outlined in an article in The Guardian newspaper.

The group also concluded that the front line of the U.S.-led invasion of Afghanistan is growing closer to the capital, Kabul.

"It is a sad indictment of the current state of Afghanistan that the question now appears to be not if the Taliban will return to Kabul but when this will happen and in what form," the Senlis report said.