Almost 4,000 US Marines launched a major offensive against Taliban on early Thursday morning in Helmand province of southern Afghanistan, the first such operation under President Barack Obama's presidency.

The U.S. troops, backed by 650 Afghan troops and police, pushed into the Helmand River valley, trying to take back the control of the poppy-growing region from the Taliban, a Marines press statement said.

Thursday's operation was different from previous ones because of the "massive size of the force", the US forces said. Similar approaches have been tried in the eastern part of the country.

In the past two months, the United States has sent 8,500 Marines to Helmand, which is the largest province in Afghanistan and considered as a Taliban stronghold.

The 8,500 is part of the 21,000 additional troops that U.S. President Barack Obama is deploying in Afghanistan to stabilize the security situation in the war-torn country. It is expected the total number of U.S. troops in Afghanistan will reach 68,000 by the end of the year.

Helmand produces more than half of the opium cultivated in Afghanistan, and is the source of about 90 percent of the global supply, according to the United Nations Office on Drugs and Crime.

(Xinhua News Agency July 2, 2009)