"We're approaching what you could actually, cautiously, term irreversible momentum in the east," Gen. Tucker said. He didn't provide any figures on that point. Eastern Afghanistan has long been a source of concern for U.S. commanders, because militants operating from havens in Pakistan's lawless border areas cross into Afghanistan to commit attacks there, increasing U.S. casualties in the area. Gen. Tucker said the Pakistani military's continuing offensive against militants in the restive Pakistani border province of Baijur had contributed to the security gains in eastern Afghanistan. He also credited a U.S.-backed pilot program that has been creating armed local militias in the area to combat the Taliban. In the south, conditions are gloomier. U.S. officials estimated that the Taliban reap hundreds of millions of dollars a year from narcotics trafficking, giving the armed group money to recruit new fighters and buy sophisticated weaponry. The Taliban also exert de facto control over many rural parts of the south, adjudicating disputes and running shadow courts and local governments. "The south is the center of gravity for the Taliban," Gen. Tucker said. The Obama administration's strategy for Afghanistan aims to stem the Taliban's momentum and reverse their territorial gains. U.S. officials said they hope the influx of new forces into southern Afghanistan will help oust the militants from local strongholds and prevent their return. The U.S. is expanding its counternarcotics efforts in the south, in an effort to make it harder for the Taliban to replenish their coffers. Gen. Tucker said U.S., NATO and Afghan forces have confiscated more drugs so far this year than in all of 2008.