The number of US troops sent to southern Afghanistan to launch a major offensive is sufficient to seize and hold areas currently under Taliban control, the top US military officer said Sunday.

"We have enough forces there now not just to clear an area but to hold it. So we can build after. That''s really the strategy," Admiral Michael Mullen, chairman of the Joint Chiefs of Staff, told CBS''s "Face the Nation."

Some 4,000 Marines launched a wide-ranging operation Thursday in Helmand province, a Taliban stronghold, in what Mullen termed "the first significant one" since President Barack Obama dispatched an additional 21,000 US troops to Afghanistan to battle a mounting Taliban insurgency allied with Al-Qaeda.

Previously, the only military forces on the ground in the area were British troops who frequently exchanged fire with Taliban militants but lacked the necessary presence to take on the insurgency.

Washington is deploying the additional forces in a bid to facilitate the development work and improved governance required to undercut local support for the Taliban.