NAWA, AFGHANISTAN »  Thousands of U.S. Marines and hundreds of Afghan troops poured into Taliban-infested villages of southern Afghanistan with armor and helicopters today in the first major operation under President Barack Obama's strategy to stabilize the country.

The offensive was launched early this morning local time 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 and 650 Afghan forces. British forces last week led similar, but smaller, missions to clear out insurgents in Helmand and neighboring Kandahar provinces.

“;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 south of the provincial capital of Lashkar Gah, in a region where no U.S. or other NATO troops have operated in large numbers.

Daybreak brought sporadic gunfire, but no heavy fighting. Medical helicopters circled overhead and landed, indicating possible early casualties among the Marines. A roadside bomb early in the mission wounded one Marine, but he was able to continue, spokesman Capt. Bill Pelletier said.

Southern Afghanistan is a Taliban stronghold but also a region where Afghan President Hamid Karzai is seeking votes from fellow Pashtun tribesmen.

The Pentagon is deploying 21,000 more troops to Afghanistan in time for the elections and expects total U.S. forces there to reach 68,000 by year's end.

That is double the number of troops in Afghanistan in 2008, but still half of much as are now in Iraq.

The Taliban, who took control of Afghanistan in 1996 and were ousted from power following a U.S.-led invasion in 2001, have made a violent comeback, wreaking havoc in much of the country's south and east.

Pelletier said troops in today's operation were sent in by a mixture of aircraft and ground transport under the cover of darkness.

The operation aims to show “;the Afghan people that when we come in we are going to stay long enough to set up their own institutions,”; Pelletier said.

Once on the ground, the troops will meet with local leaders, hear their needs, and act on them, he said.

“;We do not want people of Helmand province to see us as an enemy. We want to protect them from the enemy,”; Pelletier said.

Reversing the insurgency's momentum has been key to the new U.S. strategy, and thousands of additional troops allow commanders to push into and stay in areas where international and Afghan troops had no permanent presence.

In March, Obama unveiled his strategy for Afghanistan, seeking to defeat al-Qaida terrorists there and in Pakistan with a bigger force and a new commander. Taliban and other extremists, including those allied with al-Qaida, routinely cross the two nations' border in Afghanistan's remote south.