President Vladimir Putin launched exercises by Russia’s strategic nuclear missile forces on Saturday and Washington said Russian troops massed near Ukraine’s border were moving forward and “poised to strike”.

With Western nations fearing what could be one of the worst conflicts since the Cold War, U.S. Defence Secretary Lloyd Austin said Russian forces were beginning to “uncoil and move closer” to the border with its former Soviet neighbour.

“We hope he (Putin) steps back from the brink of conflict,” Austin told a news conference in Lithuania, saying an invasion of Ukraine was not inevitable.

Russia ordered the military build-up while demanding NATO prevent Ukraine ever joining the alliance but says Western predictions it is planning to invade Ukraine are wrong and dangerous. It says it is now pulling back. Washington and allies say the build-up is mounting.

Russian-backed separatist leaders in eastern Ukraine declared a full military mobilisation after ordering women and children to evacuate to Russia, citing the threat of an imminent attack by Ukrainian forces.