article: Concerns are growing over Russian ships that have docked in a once-secret  naval base in the Arctic. Military leaders in Norway are nervous about its powerful neighbour's presence on its 'strategically important' coastline following a spike in tensions between Russia and NATO nations. Some experts have criticised the shutting down of Olavsvern Naval Base - a huge complex buried in mountainous terrain near the town of Tromsoe - which has been closed since 2009. But fears have once again peaked after three Russian ships spent the entire winter docked deep within the mountain hideaway which was once a heavily guarded military facility. Show of strength: Norway's military leaders are growing concerned after three Russian warships spent the winter docked inside a closed naval base (file photo) deep inside the country's mountainous terrain . Aggression: In February, RAF planes intercepted two Russian bombers (file photo) which had flown into Irish territory and forced a passenger jet to divert its course . Force: And late last year, the Russian navy anti-submarine ship Severomorsk (file photo) and three other Russian ships had to be escorted out of the British channel . It was originally shut because the country's leaders thought the threat from Moscow was reduced, despite its massive Northern Fleet which is base in the nearby Kola Peninsula. Norway's former vice admiral said shutting down the base was 'pure madness' while other critics say their submarines now have to travel hundreds of extra miles to protect the region. This is far from the first time Russia has flexed its military muscles in other countries' territory. In February, a passenger plane had to be diverted to avoid two Russian bombers that flew through Irish-controlled airspace without warning. The disruption on February 18 was thought to have occurred during the same incident in which British RAF Typhoon fighters were scrambled to escort the Russian vessels. That move was perceived as a show of strength by Russian President Vladimir Putin over the Ukraine conflict after Prime Minister David Cameron accused him of challenging the 'territorial integrity' of Kiev. It followed a separate incident when the Royal Navy had to intercept a Russian warship which strayed to close to the UK while passing through the English channel the same month. The Neustrashimy-class warship – equipped with missiles, anti-aircraft guns and torpedoes – was monitored and escorted by a heavily-armed British frigate. Cat and mouse: Heavily-armed HMS Argyll follows the Russian warship (back left) as it passes through the English Channel in February . Intercepted: Footage released on Russian TV showed the moment two RAF jets escorted the Russian bomber in February . Concerned: They are worried by this perceived show of strength from Moscow (Russian President Vladimir Putin pictured) and its presence on its 'strategically important' coastline . And late last year, the HMS Tyne had to escort another Russian destroyer and three other boats from the Channel as they passed through the Strait of Dover after carrying out military exercises in the North Sea. Since January 2014, there have been at least 17 shows of military strength by Russia near the UK. The most serious included: . Feb 18: RAF jets scrambled after two Russian Bear bombers spotted off the coast of Cornwall, forcing a flight from Dublin to divert. Feb 15: Russian warship intercepted by Royal Navy in the English Channel. Jan 28: RAF fighters challenge two Russian bombers capable of carrying nuclear missiles south of Bournemouth. Jan 8: Defence chiefs ask for US help to hunt a suspected Russian submarine lurking off the coast of Scotland. Nov 2014: Russian flotilla on military exercise in the Channel escorted from UK waters by HMS Tyne. Nov 2014: Nato aircraft called in to hunt suspected Russian submarine off the west coast of Scotland. Oct 2014: RAF Typhoon warplanes shadow two Bears as they fly down the west coast of Britain. Elinar Skorgen added: 'We are the only country along with Russia to have a permanent presence in the Barents Sea, where we share a common border. Obviously our navy should be stationed there, including our submarines. If the ships aren't there where they are needed, they might as well be scrapped altogether.' The Armed forces put the base - which cost over £390million to construct - up for sale on Norway's version of eBay. It was eventually bought for just £3.5million by a Norwegian businessmen and was rented out to Russian research vessels which were reportedly linked to the country's state-owned energy giant Gazprom. Its landlord Gunnar Wilhelmsen said: 'There are no longer any secrets surrounding this base... Not since the military and NATO agreed to put it on sale over the Internet, along with photographs of every nook and cranny.' Many military experts are now worried by the the potential for Russian military activity aboard the research vessels. A former second in command for the Norwegian military said: 'Russia is a country where the state has a say over all commercial or semi-state business. It's clear, very few people know what happens on these vessels.' Jan Reksten believes the sale of Olavsvern was 'a double loss' as 'Norway's armed forces lost an important base and now there are Russian vessels docked there'.
highlights: Three Russian ships that docked in Olavsvern Naval Base for the entire winter .
  Base which was shut down in 2009 is nestled deep inside mountainous region .
  Norway's military fears Russian presence on 'strategically important' coastline .
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