* Commission says military planes turn communications off
* NATO has accused Russia of endangering civilian flights
BERLIN, Dec 8 (Reuters) - The European Commission has asked aviation safety officials to examine several near mid-air collisions in recent months between passenger planes and military aircraft flying without transponders on to identify them.
The European Aviation Safety Agency (EASA) said on Monday that European Union members reported military planes were flying close to civilian aircraft over the sea above EU borders and "it was not possible to establish radio contact with them".
The EASA statement gave no other details, but it came a week after the U.S. ambassador to NATO accused Russian military aircraft of endangering civilian flights in Europe by turning off their communications and failing to file flight plans.
NATO - the North Atlantic Treaty Organisation - said last month that planes from its member states had to scramble 400 times this year in response to an increase in Russian air activity around Europe not seen since the Cold War.
"The support of EASA will be essential in further identifying appropriate solutions and follow-up measures to address such events at the European level," the EASA statement quoted Joao Aguiar Machado, the Commission's director general for mobility and transport, as saying.
An EASA spokesman said details of the flights in question would be clarified as part of the investigation, which would deliver its recommendations to the Commission in March 2015.
Moscow has intensified its air activity around Europe this year and beefed up its military forces on the Crimean peninsula, which it annexed from Kiev in March.
Tensions rose after a Malaysian airliner was downed over eastern Ukraine in July. Western experts say it was most likely shot down by a ground-to-air missile fired from territory held by pro-Russian separatists. Moscow denies it supports them.
The Norwegian military earlier this month released footage showing an apparent close encounter between a Russian and Norwegian fighter jet.
"This is a very serious issue," EASA executive director Patrick Ky said in a statement. "We will consult and interview all the relevant civil and military bodies in order to gather the necessary information to complete our analysis." (Reporting by Victoria Bryan, Tim Hepher and Julia Fioretti; Editing by Tom Heneghan)