Washington, July 2 The US Thursday launched a massive operation, considered one of the largest since the Vietnam war, against the Taliban in Afghanistan’s southern Helmand province as part of a new initiative under President Barack Obama.

About 4,000 US marines and 650 Afghan troops, supported by NATO combat aircraft, are taking part in the offensive.

US Brigadier General Larry Nicholson said the operation is different from the previous ones in Afghanistan because of the “massive size of the force”.

Officers on the ground said it was the largest marine offensive since Vietnam and first major operation under Obama.

The operation began after troops moved into the Helmand river valley early Thursday with helicopters and heavy transport vehicles, the Online news agency reported.

Southern Afghanistan is considered a stronghold of the Taliban.

“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,” Brig Gen Nicholson said in a statement.

“One of the most critical things is to tell people why we’re there, and we are going to have a limited opportunity to gain their trust,” the US general said.

The operation aims to improve the security situation in the country ahead of the Afghan presidential elections Aug 20.

US military spokesman captain William Pelletier told the BBC that there had been “no enemy contact” in the first hours of the operation, but one marine was injured in a blast.

He said the military was prepared for the casualties, but stressed: “It is absolutely essential no civilians be harmed.”

Helmand Governor Gulab Mangal said the operation will be “very effective”.

“The security forces will build bases (in Helmand) to provide security for the local people so that they can carry out every activity and take their lives forward in peace,” he said.

Currently, there are more than 61,000 foreign soldiers from 42 countries, including the US, Canada, Australia, Britain and other European countries, as part of the NATO’S International Security Assistance Force. The US is the largest contributor, with over 28,000 soldiers.

President Obama has pledged to send an additional 21,000 soldiers to Afghanistan to train the Afghan security forces, besides conducting counter-insurgency operations.