"At this point we have made significant progress, but we are not yet at the point where it [Afghan democracy] is completely sustainable," the BBC Wednesday quoted Dunford as saying.
Dunford oversees the withdrawal of troops with NATO's International Security Assistance Force, which is expected to hand over full responsibility for Afghanistan's security to the country's own forces by the end of 2014.
Afghan forces are "getting good enough," he said, but talks with the Taliban are essential for the country's future as many criminal groups are also working with the Islamist militant group.
In a message directed to the Taliban, the general said "to the degree that they have any kind of political space to accommodate with the Afghan people, now would be the time."
The last districts in the country still under NATO control are scheduled to be handed over to the full control of Afghan troops next week. Some international troops will remain in a support role.