Gen. David Petraeus warned Tuesday of "tough months ahead" as the U.S. steps up its presence in Afghanistan to help stabilize the country.
Petraeus, who heads U.S. Central Command, said the U.S. faces a reinvigorated Taliban insurgency and a rise in the trafficking of illegal narcotics, which he said helps fuel the insurgency.
The top goal, he said, is helping prevent Afghanistan from sliding to its pre-9/11 days that allowed the country to become a safe haven for al-Qaida leaders plotting attacks.
Getting there won't be easy, he said.
"We are going to make progress but it's going to get worse before it gets better," Petraeus said. "When you go into an enemy's territory ... they are going to fight you for it."
President Barack Obama has ordered an additional 21,000 U.S. troops to Afghanistan this summer to bolster the record 38,000 already in the country.
Petraeus is credited for crafting the surge strategy that helped turn the tide and reduce violence in Iraq, a turnaround that he said hinged on a series of "big ideas," the most important of which was a strategic shift that had U.S. troops spending more time living and working closely with Iraqi citizens.
Under the new strategy, the goal was not simply to clear an area of insurgents, but to try to bring some stability in the aftermath of any raid.
"You can't commute to the fight," he said. "You can't clear and leave. You have to clear and hold, and then build."
Another important lesson was sorting out insurgents who could be convinced to join the county's political process from those hardcore "irreconcilables" who were dedicated to their cause and couldn't be flipped.
Failing to learn that lesson early on, and failing to invest more directly in the rebuilding of the country, helped allow the violence in the country to escalate dangerously before the surge, he said.