Russia's increased military presence in the Baltic Sea area, including its air force, has prompted some officials to compare it to the Cold War. Here's a summary of the most serious incidents reported across the region.

ESTONIA

NATO member Estonia says Russian aircraft have violated its airspace six times this year, a sharp increase compared to previous years.

The most serious incident happened on Oct. 21, when a Russian Ilyushin-20 surveillance aircraft crossed into Estonia's airspace for about a minute near the island of Saaremaa. Estonia summoned Russia's ambassador to lodge a formal complaint.

Another example took place near the island of Vaindloo in the Gulf of Finland near a corridor where Russian military planes fly to get from the St. Petersburg area to the Russian outpost of Kaliningrad, which is wedged between Poland and Lithuania.

LATVIA

Latvia hasn't seen any airspace violations by Russian aircraft this year. But Latvia's Defense Ministry says it has recorded more than 180 incidents of Russian military planes straying "dangerously close" to Latvia's airspace without identifying themselves.

Defense Ministry spokesman Kaspars Galkins said Russian military planes, as a rule, fail to submit flight plans and have switched off their transponders.

LITHUANIA

No airspace violations by Russian aircraft so far this year, but Defense Ministry says Russian activity close to Lithuania's airspace has grown substantially.

Lithuania says Russia's military flights violate International Civil Aviation Organization regulations and pose a risk to civil aviation by failing to report flight plans, ignoring civilian air traffic controllers and switching off their on-board transponders.

On March 27, 2012, an SU-27 Russian fighter plane entering from Kaliningrad strayed some 12 kilometers (8 miles) into Lithuania's airspace, the Defense Ministry says.

FINLAND

On Aug. 28, a Russian AN-72 transport plane briefly entered Finnish airspace over the Gulf of Finland. Finland's defense minister, Carl Haglund, said he suspected that was intentional and he demanded an explanation from Moscow. The Finnish Border Guard said the flight plan indicated the Russian carrier Aeroflot as being the transport flight's operator.

Two other Russian violations of Finland's airspace occurred a few days earlier, involving a Tupolev TU-134 jet and an AN-26 cargo plane.

SWEDEN

Last month the non-NATO member launched its first submarine hunt since the collapse of the Soviet Union. Sweden said a small, foreign submarine entered its waters illegally but never found it and didn't disclose its nationality.

Sweden's armed forces say foreign aircraft — including Russian and NATO planes — have breached Swedish airspace 10 times this year, up from eight last year and seven in 2012.

On Sept. 17 two Russian SU-24 bombers crossed the border south of Oland island for about 30 seconds, leaving only after Swedish air force fighters approached them.

Sweden's military says its own spy planes flying over the Baltic Sea have been approached by Russian planes flying unusually close. But it's not just Russian aircraft. On July 18, an American spy plane entered Swedish airspace to avoid Russian military planes.

DENMARK

No airspace violations recorded, but on March 3 an SAS passenger jet taking off from Copenhagen Airport nearly collided with a Russian spy plane. This happened in international airspace near Sweden, and its investigators said the Russian plane came within 100 meters (300 feet) of the SAS plane. The Ilyushin-20, flying without transponders, wasn't registered by civilian air traffic controllers.

POLAND

Polish officials reported one air space violation in April by a military aircraft of a foreign country, and a NATO military official identified it as a Russian aircraft.