Ukraine v Russia militaries - in 60 seconds
4 June 2014 Last updated at 10:13 BST
Nato defence ministers are meeting in Brussels to discuss the long-term security implications of Russian actions over Ukraine.
Kiev and the West have accused Russia of stirring up separatist sentiment in parts of eastern Ukraine where the majority are Russian-speaking.
Russia, which denies the claims, wants the UN Security Council to call for an immediate end to fighting in east Ukraine, where insurgents have seized two government bases near the city of Luhansk.
Russia is estimated by Nato to have some 40,000 troops near Ukraine's border, though Moscow says they have been pulled back.
BBC News compares the military strengths of the two countries, in 60 seconds.
Video produced by Jasmine Coleman