World leaders believe time is running out to avert a full-scale invasion by Russia of Ukraine.
Moscow has sent tens of thousands of troops to its border with its ex-soviet neighbor and western leaders are convinced an invasion is imminent.
Speaking with more certainty than in recent weeks, Joe Biden said on Friday that Vladimir Putin has made the decision to invade Ukraine “within days”, including a targeted attack on the capital Kyiv.
The US President said diplomatic outreach to the Russian president had failed and troops were set to move on Ukraine within the week.
Mr Biden has warned Moscow against a “catastrophic and needless war of choice” and said the US and its partners “are prepared to defend every inch of Nato territory.”
Here we break down how the crisis reached this point and what could be next.
As many as 190,000 Russian troops are currently “in and around Ukraine”, according to Michael Carpenter, the US ambassador to the OSCE.
The Russian troops have massed alongside 1,200 tanks, fighter jets and long-range missile batteries, sparking the biggest crisis in East-West ties since the Cold War.
Russia said on February 16 that military drills in Moscow-annexed Crimea had ended and that soldiers were returning to their garrisons, a day after it announced a first troop pullback from Ukraine’s borders.
But, on February 18, UK Home Office minister Damian Hinds told Times Radio: “There are many, many troops built up on the Ukrainian border. There is no sign of that falling back, contrary to what has been claimed.
“Troops remain in place and there could be an invasion, there could be an incursion at any time, but it could also take longer.”
Russia has put forward a list of security demands including a guarantee that Ukraine will never be allowed to join Nato and that alliance forces pull back in Eastern European countries that joined after 1997.