Speaking to the Senate Armed Service Committee in Washington, Dunford questioned why the American presence in Afghanistan has a hard deadline of 2017 for full withdrawal.
"All of us in uniform, including the Afghans, would have preferred that had been a bit more ambiguous," he said.
Under his command of the International Security Assistance Force, the number of U.S. troops fell, over 18 months, from 100,000 to 30,000. It is expected to drop to 9,800 by the end of 2014, as Afghan forces increase their involvement in fighting the Taliban. A security agreement between Afghanistan and the United States -- to keep U.S. troops in the country past the end of the year -- has not yet been signed.
When asked if al-Qaida and similar militant groups could return to Afghanistan after the departure of U.S. troops, Dunford called that possibility "significant."
"There's no doubt that the Afghan forces of today are not capable of conducting the operations we're conducting today," he said.
Notable deaths of 2014 [PHOTOS]
Syrian Al Qaida group executes Lebanese soldier