Recent close shaves between Russian fighters and civilian aircraft highlight the dangers of the cat-and-mouse game being played out between Moscow and the West in European skies amid the crisis in Ukraine, analysts say.

In the latest incident, Sweden said Friday that a Russian military jet nearly collided with a passenger plane south of Malmoe shortly after take-off from Copenhagen International Airport.

Both countries called in their Russian ambassadors to protest, only to be told that a huge increase in Russian military activity in recent months was "a response to NATO's activities and escalation in the region."

Russia later accused Swedish authorities of being under the influence after smoking too much cannabis.

But such incidents are no joke for European authorities, with memories still fresh from the shooting down of Malaysia Airlines flight MH17 over Ukraine by a missile that the West alleges was fired by pro-Russian separatists.

The European Aviation Safety Agency (EASA) has begun an investigation into a series of near-misses with Russian military aircraft not using the transponders which identify them and tell other planes of their position.

This practice is particularly dangerous, analysts said.

- Transponders turned off -

"While Russia claims that its military aircraft remain in international airspace, to do so while turning off transponders and swooping close to other aerial platforms is very dangerous," Brooks Tigner, chief editor and policy analyst at Security Europe, told AFP.

"That is disruptive to accepted international air safety rules and a risky game for Russia to play," Tigner said.

NATO aircraft, in contrast, usually keep their transponders on, he said.

"Safety is the top priority for aviation," the International Air Transport Association said.

"There are clearly established rules to ensure the safety of all aircraft when flying in controlled airspace. One of these is that all aircraft -- military and civil -- should have functioning transponders."

Russia and US-led NATO each stepped up their military activity and readiness as the Ukraine crisis plunged ties into a deep freeze reminiscent of the worst days of the Cold War.

A key development is that an increase in defence spending since 2008 has given Russia upgraded aircraft, said Douglas Barrie, military aerospace expert for the International Institute for Strategic Studies in London.

NATO has reported a "substantial increase" in Russian operations, with nuclear-capable bombers and fighter escorts out in force over the Baltic Sea and ranging far and wide into the Atlantic, prompting scores of intercepts by alliance aircraft along the way.

- Fears of disaster -

Video footage has shown some very close encounters and stoked fears of a serious misunderstanding or even a repeat of Cold War disasters such as the Russian shooting down of a South Korean passenger jet in 1993 with the loss of 269 lives.

Complicating the situation is the fact that because planes have avoided Ukraine's airspace since MH17 in July, air traffic in some other neighbouring regions has soared by more than 20 percent, according to Eurocontrol, the air traffic management organisation.

NATO foreign ministers agreed earlier this month that "at this time of tension there is a need for regular communications among NATO and Russian military to avoid any incidents."

"NATO military authorities should keep channels of military communications open and use them when necessary to avoid any possible misunderstandings related to military activities," it said.

The trouble is that Russia has not shown any interest in dialogue so far, the alliance said, and worryingly, there had not been any direct contact with Russia's top brass for more than six months.

Analysts said there is unlikely to be any immediate improvement in the situation.

"Russian and NATO aircraft have dogged each other for years but they always know where the other is because their radars lock on to the opponent with precision," said Tigner of Security Europe.

"This cat-and-mouse game is par for the course. The risk of escalation here is more political than military."