The joint Afghan-NATO assault against Taliban bastion in southern Afghanistan is just the beginning of a long campaign, which may last up to 18 months, a top U.S. commander said on Sunday.

15,000 Afghan and the NATO-led troops including 5,000 U.S. Marines launch military operation against Taliban in Marjah district of southern Helmand province. [Xinhua]

"This is just the initial operation of what will be a 12 to 18- month campaign as General McChrystal and his team mapped it out," David Petraeus, head of the U.S. Central Command, told NBC television's "Meet the Press" program.

Operation Moshtarak or Together, with the involvement of 15,000 Afghan and the NATO-led troops including 5,000 U.S. Marines, was launched a week ago against the Taliban bastion in Marjah district of southern Helmand province to restore government's authority there.

"We spent the last year getting the inputs right in Afghanistan, getting the structure and organizations necessary for a comprehensive civil military campaign, putting the best leaders we can find in charge of those," said Petraeus.

The operation was seen as a major test of U.S. President Barack Obama's new strategy on Afghanistan, which calls for sending 30, 000 more troops to the country and starting pulling out U.S. forces in July 2011.