AUCKLAND - The last of the 33,000 'surge' troops ordered into Afghanistan by President Barack Obama in 2009 have withdrawn from the country, returning the American presence to pre-surge levels, a senior US defense official said on Friday.

The surge in American troops was designed to push back the Taliban and create space for NATO forces to build the Afghan army to a point where it could take over Afghanistan's security, allowing for an eventual Western drawdown.

The completion of the surge withdrawal had been expected by the end of September. Obama has trumpeted ending the war in Iraq and winding down the war in Afghanistan as he seeks re-election on Nov. 6.

The return of US forces to pre-surge levels comes as NATO commanders wrestle with an upswing in "insider attacks" by Afghan forces turning their guns on Western troops.

NATO announced this week it was scaling back some joint operations with Afghan troops as a result, raising questions about Obama's plan to stabilize the country ahead of the expected withdrawal of most combat troops by the end of 2014.