In a speech, Petraeus said NATO's strategy in Afghanistan had not changed.
"We must help Afghan leaders develop their security forces and governance capacity so that they can, over time, take on the tasks of securing their country and see to the needs of their people," he said. "And, in performing these tasks, we clearly must pursue the insurgents relentlessly."
Petraeus said the war had reached a "critical moment."
"We must demonstrate to the Afghan people, and to the world, that al Qaeda and its network of extremist allies will not be allowed to once again establish sanctuaries in Afghanistan from which they can launch attacks on the Afghan people and on freedom-loving nations around the world," he said.