The United States has warned Russia not to invade Ukraine and urged both countries to return to a set of agreements designed to end a separatist war by Russian-speakers in eastern Ukraine. Here is a look at the agreements, which were signed in Minsk in 2014 and 2015.
Ukraine and the Russian-backed separatists agreed a 12-point ceasefire deal in the capital of Belarus in September 2014.
Its provisions included prisoner exchanges, deliveries of humanitarian aid and the withdrawal of heavy weapons, five months into a conflict that by that point had killed more than 2,600 people – a toll that has risen to more than 14,000 now, according to the Ukrainian government.
The agreement quickly broke down, with violations by both sides.
Representatives of Russia, Ukraine, the Organisation for Security and Cooperation in Europe (OSCE) and the leaders of two pro-Russian separatist regions signed a 13-point agreement in February 2015 in Minsk.
The leaders of France, Germany, Russia and Ukraine gathered there at the same time and issued a declaration of support for the deal.
The deal set out a series of military and political steps that remain unimplemented.