This European force could undermine NATO, particularly if it has a separate headquarters and planning staff.

FORBES: Put it where it belongs

Indeed, the first thing Nato ministers will be doing is huddling with their chiefs of staff at a secret US base just outside Colorado Springs for a "study seminar".

BBC: NEWS | Americas | Nato studies future tasks

General Stan McChrystal, Gen Petraeus' predecessor as Nato commander in Kabul, also suffered a public fall from grace in 2010, stepping down after staff members were quoted by Rolling Stone magazine being critical about the Obama administration.

BBC: Petraeus' downfall - a modern morality tale

On being promoted to colonel he was appointed to chief of staff 1st (UK) Armoured Division in 1995 before returning to Bosnia a year later as part of Nato's Peace Implementation Force (IFOR) for a further six-month tour.

BBC: Profile: Major General John McColl