Thousands of NATO and Afghan troops are expected to launch Operation Mushtarak in the Marjah district of southern Helmand province. The operation is predicted to be the largest ever since 2001 when the United States waged the war on terror in Afghanistan.

NATO and Afghan officials have urged militants holding Marjah, to lay down their arms.

The precise date of the assault has been kept secret.

On Tuesday, US soldiers launched a preliminary operation in support of the planned offensive on Marjah, the largest Taliban-controlled town in southern Afghanistan.

Larry Nicholson, US Brigadier General, said, "Now there's some neighborhoods we're going to go into where you better button your chin strap because you're going to have a long day. But there's only one place we won't go and that's a place called Marjah, and we're about to take care of that real quick."

On the same day, British forces bound for Afghanistan took part in a series of combat exercises on Salisbury Plain in southwest England.

Brigadier Richard Felton, British Army, said, "But really we're carrying on the trend followed by General McChrystal as he stressed last year in June when he took over of really protecting the population, conducting population-centric counter-insurgency in partnership with the Afghan national security forces."

Officials say the purpose for the upcoming massive offensive in southern Afghanistan is not for military success, but to bring security, development and good governance to the region.