Some 7,000 of the new U.S. troops ordered to Afghanistan are fanning out across the dangerous Afghan south on a mission to defeat the Taliban insurgency and to change the course of a war claiming American lives at a record pace.

The Marines represent the first wave of 21,000 troops ordered to Afghanistan this summer by U.S. President Barack Obama. Most of the buildup will take place in Helmand and Kandahar. The two southern provinces lie at the heart of the insurgency and are close to the border with Pakistan, where the Taliban's top leadership is believed to be based.

Some 7,000 Marines from the 2nd Marine Expeditionary Brigade, based at Camp Lejeune, N.C., are now in the country, Marine spokesman 1st Lt. Abe Sipe said. The forces have brought fighter aircraft, transport helicopters, artillery and the infrastructure needed to support what will ultimately be a force of about 11,000.

Helmand province — the world's largest opium poppy-growing region — is also Afghanistan's most violent.

"This is where the fight is, in Afghanistan," said 1st Sgt. Christopher Watson, who like many here has also served in Iraq. "We are here to get the job done."

Taliban militants and the drug lords they protect are believed to reap hundreds of millions of dollars from Afghanistan's drug trade. U.S. and NATO troops have stepped up attacks this year on drug labs after concluding the drug trade and the insurgency are intertwined.

Most of the newly arrived Marines are now stationed at Camp Leatherhead, a small base in Helmand expanding by the hour as workers build permanent structures. Some Marines have moved out to smaller outposts and are patrolling Helmand's deserts under a harsh summer sun.

Commanders warn that U.S. deaths are likely to increase this summer, the traditional fighting season in Afghanistan.

At least 70 American troops have been killed in Afghanistan this year, according to an Associated Press count, a 75 per cent increase over the 40 U.S. troop deaths through the first week in June last year. A record 151 American forces died in Afghanistan in 2008.

The Afghan government controls some of the major towns and roads in Helmand, but most of the province of about one million is under the sway of the Taliban. Thousands of British forces have been deployed in Helmand since mid-2006, too few to provide security and counterinsurgency operations for the entire province.

Canada has about 2,500 troops in Afghanistan, with the majority in Kandahar province.