Russian President Vladimir Putin has said NATO is one of Russia's biggest dangers. NATO is a North American and European defence treaty. Countries guarantee to act if any member state is threatened. Tensions between Russia and NATO started after the end of WWII. The rival, Russian-led Warsaw Pact started in 1955 and led to the Cold War intensifying. Relations worsened again last week when former Russian ally Ukraine made new efforts to join NATO. Russia accused NATO of using Ukraine as a "frontline of confrontation".
Mr Putin said that for the first time, Russia would use conventional weapons "as part of strategic deterrent measures" if Russia is under threat. A NATO spokeswoman said the NATO was following international law over Ukraine and was not threatening Russia. She said NATO will assess Ukraine's readiness to join the alliance in the same way as with any other country. She added: "This is an issue between NATO and the individual countries aspiring to membership." She said Russia's actions in Ukraine were breaking international law and threatening European security.