US General David Petraeus said he had expanded the authority of the top commander in Afghanistan, General Stanley McChrystal, to give him operational control over nearly all American forces in the country.

Officials in Washington said the move was meant to further streamline the military hierarchy under McChrystal as the top US and Nato commander in Afghanistan and to achieve greater unity of effort.

 Petraeus' order mainly expands McChrystal's control over Marine elements and Special Operations forces, giving him 'operational' as well as 'tactical' control, officials said.   

A small number of Special Ops forces, a US joint task force that oversees US detainee operations and a handful of other troops will still be outside McChrystal's operational control as the top Nato commander. But they will be under his control as the commander of US forces in Afghanistan.

Special Ops have come under particular scrutiny since a Nato airstrike late last month killed 27 Afghan civilians. US officials say Special Ops called in the strike.

McChrystal has sought to curtail the use of air power, arguing that civilian deaths hurt a campaign to win over the local population and defeat Taliban insurgents, a theme Petraeus echoed during his remarks on Thursday.

Speaking to a defense conference in Ottawa, Petraeus said he had ordered that 'all US forces, less a handful, be placed there under General McChrystal's operational, not just tactical, control.'    

As head of US Central Command, Petraeus oversees wars in Afghanistan as well as Iraq. He said his order consolidating command under McChrystal was issued within the past week after 'considerable discussion ... within the US Department of Defense.'    

'This is a significant development. It will provide General McChrystal authorities that I never had as the commander in Iraq ... and that his predecessors never had in Afghanistan either,' Petraeus said.

McChrystal's counterinsurgency strategy emphasizes seizing population centers and avoiding combat in built-up areas whenever possible to avert civilian deaths. The number of civilians killed by Nato troops has fallen since he took command in mid-2009. - Reuters