Russia has completed Burevestnik, according to a classified alliance document.
NATO officials are sounding the alarm after Russia reportedly completed development of its nuclear-powered Burevestnik cruise missile, a system Western intelligence views as a major challenge to alliance defences.
The missile, known within NATO as the SSC-X-9 Skyfall, is described as highly manoeuvrable, mobile and capable of travelling at more than 900 km/h.
