Ukraine's armed forces find themselves vastly outnumbered and outmatched in firepower by their Russian opponents, despite growing military assistance for Kyiv's troops by the West.
From Russia's massing of soldiers along the border in November to Vladimir Putin ordering troops into eastern separatist areas, here is a timeline of months of tensions around Ukraine.
Russian parliament's upper house on Tuesday voted to allow President Vladimir Putin to use the Russian army outside the country to support separatists in Ukraine.