The shape of the Afghan conflict is shifting, as U.S. reinforcements have brought hints of progress along the porous eastern border with Pakistan, while security conditions in southern Afghanistan continue to deteriorate, according to U.S. officials. Senior American commanders say they believe the war may be won or lost in southern Afghanistan, a Taliban stronghold and one of the world's largest opium-producing regions, where an estimated 80% of Afghanistan's insurgent violence occurs. A shortage of U.S. forces has allowed the Taliban to create safe havens in the south. "We're at a stalemate" in the south, said U.S. Maj. Gen. Michael Tucker, deputy chief of staff for operations for the American-led North Atlantic Treaty Organization force in Afghanistan. He didn't provide figures on worsening violence. "We just simply do not have enough forces to address the needs of the people down there," he said by video link from Kabul. "The enemy, obviously, is taking advantage of that posture." More than 21,000 new U.S. forces are expected to deploy to Afghanistan in coming months. The addition will push U.S. troop levels there to about 65,000, their highest since the start of the war in 2001. Most of the reinforcements will be sent to southern Afghanistan, where the U.S. and its allies are preparing a major offensive against the Taliban. About 4,000 American reinforcements deployed to eastern Afghanistan earlier this year, and senior U.S. commanders said they believe the additional troops helped to improve security conditions in the volatile region. "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.