Thousands of U.S. Marines poured from helicopters and armored vehicles into Taliban-controlled villages of southern Afghanistan Thursday in the first major operation under President Barack Obama''s strategy to stabilize the country.

The offensive was launched shortly after 1 a.m. Thursday local time (4:30 p.m. EDT Wednesday, 2030 GMT Wednesday) in Helmand province, a Taliban stronghold and the world''s largest opium poppy producing area. The goal is to clear insurgents from the hotly contested region before the nation''s Aug. 20 presidential election.

Officials described the operation, dubbed Khanjar, or "Strike of the Sword," as the largest and fastest-moving of the war''s new phase and the biggest Marine offensive since the one in Fallujah, Iraq, in 2004. It involves nearly 4,000 newly arrived Marines plus 650 Afghan forces. British forces last week led similar, but smaller, missions to clear out insurgents in Helmand and neighboring Kandahar province.

"Where we go we will stay, and where we stay, we will hold, build and work toward transition of all security responsibilities to Afghan forces," Marine Corps Brig. Gen. Larry Nicholson said in a statement.

Transport helicopters carried hundreds of Marines into the village of Nawa, some 20 miles (30 kilometers) south of the provincial capital of Lashkar Gah, in a region where no U.S. or other NATO troops have operated in large numbers.