NATO warns Russian military behaviour is undermining decades of trust Tensions between NATO and Russia are on the rise following a spike in Russian air force activity in Eastern Europe and its troop movements close to Ukraine's border. At a joint meeting with the EU's new foreign chief, Frederica Mogherini . NATO's Secretary General Jens Stoltenberg said recent Russian behaviour was unacceptable: "Russia continues to support the separatists by training them, by providing equipment and supporting them by also having special forces, Russian special forces inside parts of Ukraine," said Stoltenberg The recent Russian air activity, while keeping to international airspace over the Baltic and North Seas, has flirted close to airspace borders. US Air Force General Philip Breedlove, speaking at the Pentagon said: What you saw that past week was a larger, more complex formation of aircraft carrying out a little deeper and I would say a little more provocative flight path. For its part Russia has expressed its own concerns over NATO enlargement and its reinforcement of troops in Eastern Europe. Although NATO says the alliance is not back on Cold War terms with its former enemy, it believes Russian behaviour is undermining trust built up over decades.