Dmitry Medvedev, Russia’s incoming president, has warned that granting Nato membership to the former Soviet republics of Ukraine and Georgia could threaten European security.

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His comments, in an interview with the Financial Times, will step up pressure on the alliance not to allow the two states to join Nato’s “membership action plan” at a summit in Bucharest next week. Vladimir Putin, outgoing Russian president, is due to attend part of the summit.