Russia's Vladimir Putin has said NATO is one of Russia's biggest dangers. NATO is a North American and European defence treaty that started in 1949. It created tensions between Russia and the West that started the Cold War. The rival Warsaw Pact began in 1955 and the Cold War got worse. Relations worsened last week when former Russian ally Ukraine tried to join NATO. Russia said NATO was using Ukraine as a "frontline of confrontation".
NATO said it was following international law over Ukraine and was not threatening Russia. It said it would look at how ready Ukraine is to join the alliance. It would do this in the same way as with any other country. A spokeswoman said: "This is an issue between NATO and the individual countries aspiring to membership." She added that Russia's actions in Ukraine broke international law and threatened European security.