Joe Biden has told Vladimir Putin to stand down in Ukraine as the two leaders shared a phone call today amid a massive build-up of Russian troops on the border.

Biden 'voiced concerns over the sudden Russian military build-up in occupied Crimea and on Ukraine's borders, and called on Russia to de-escalate tensions', the White House said after the call.

He spoke of his 'unwavering commitment to Ukraine’s sovereignty and territorial integrity' and proposed a summit 'in the coming months', the White House said, without giving any indication of Putin's response.