Washington (CNN) -- America's top military officer painted an upbeat picture Wednesday of progress in Afghanistan. But the Joint Chiefs chairman, Adm. Mike Mullen, cautioned that recent successes are fragile and future advances will be costly.
"The enemy is being pushed out of population centers. He's being denied sanctuary. And he's losing leaders by the score," Mullen said Wednesday.
But he told reporters that the U.S. and allies must press ahead and redouble their efforts. The United States added 30,000 troops in 2010.
"We know the gains we have made are tenuous and fragile and can be lost," Mullen said. "We know the enemy is resilient. And we know that things are likely to get harder before they get any easier."
Mullen said his firsthand look during visits to Kandahar and Helmand provinces convinced him that the local population is rejecting what he called Taliban scare-tactics.
"Those very citizens are taking back their own towns and villages, building schools and roads, harvesting alternative crops, and in general contributing to a growing sense of safety in parts of the south," he said.
The next phase, pushing into areas controlled by Taliban fighters, will be difficult.
"We must prepare ourselves for more violence and more casualties in coming months," Mullen said. "The violence will be worse in 2011 than it was in 2010 in many parts of Afghanistan."