Story highlights NATO: More than 19 instances of Russian aircraft in European airspace in 24 hours 
 
 Groups of Russian aircraft detected over areas of Baltic, North, Black seas 
 
 NATO: "Unusual level of air activity over European airspace" 
 
 NATO official tells CNN the recent flights could be possible prelude to Russian air exercises 
 
 An "unusual" uptick in the size and scale of Russian aircraft flying throughout European airspace in recent days has raised alarm bells for NATO officials that come amid other provocations already rattling the West. 
 
 Multiple groups of Russian military bomber and tanker aircraft, flying under the guise of military maneuvers, were detected and monitored over sections of the Baltic Sea, North Sea and Black Sea on Tuesday and Wednesday. 
 
 Those flights represented an "unusual level of air activity over European airspace," according to a press release from NATO. 
 
 Adding to the concern -- none of the Russian aircraft filed customary flight plans or maintained radio contact with civilian aviation authorities or used any of their onboard transponders. 
 
 "This poses a potential risk to civil aviation as civilian air traffic control cannot detect these aircraft or ensure there is no interference with civilian air traffic," NATO said in its release. 
 
 That concern was echoed by a U.S. official speaking with CNN who noted that none of any recent interactions between U.S. and Russian aircraft have proved problematic to this point. 
 
 NATO said that in a 24-hour period ending late Wednesday, there were more than 19 instances of Russian aircraft in European airspace. 
 
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 According to NATO, Norwegian F-16s were scrambled and intercepted eight Russian aircraft flying over the North Sea. While some of the aircraft turned back toward Russia, two Tu-95 Bear H Russian bombers continued their flight, and were identified and intercepted by F-16s from Portugal. 
 
 British fighters were also scrambled in response as the two Russian planes continued their flight westward over the Atlantic Ocean. 
 
 NATO said the two Russian planes subsequently resumed a flight path back toward Russia but said those two planes were still airborne at the time of the press release. 
 
 A NATO official tells CNN the alliance believes the recent flights are a possible prelude to unannounced Russian air exercises. 
 
 But while officials have noted a near-constant pattern of Russian military flights throughout NATO airspace over the past weeks, officials observed there has been little provocative behavior -- like buzzing or rollovers -- by Russian pilots in their encounters with NATO aircraft. 
 
 The latest incidents also come at a time when international calls for Russia to de-escalate some of its actions beyond its borders do not appear to be taking hold. 
 
 Russia's continued support for separatist rebels in eastern Ukraine, along with plans to recognize a controversial election by the rebels next month are likely to keep the sanctions by the EU and the United States in place against Russia for the time being. 
 
 And a reported hack of an unclassified computer network used by the White House and is believed to have originated from Russia according to two U.S. officials with knowledge of the breach. ||||| NATO intercepted at least 19 Russian aircraft flying far outside Russia's airspace today, worrying the organization's officials. 
 
 "These sizable Russian flights represent an unusual level of air activity over European airspace," NATO said in a statement released this afternoon. 
 
 The Russian fighter jets and bombers were seen flying in three different regions. The intercepts came a week after widespread reports that a Russian submarine may have been spotted off the coast of Sweden. 
 
 The North Sea and Atlantic Ocean had the largest fleet of Russian aircraft activity, with eight planes detected by NATO radar flying in formation from Russian airspace toward the Norwegian Sea and into international airspace this afternoon. 
 
 NATO allies, which continually watch over partner airspace, saw six of the planes turn back towards northern Russia after Norwegian Air Force F-16s intercepted the planes. The remaining two Russian planes, both Tu-95 Bear H bombers, continued to fly above the Norwegian coastline, prompting NATO planes stationed in the United Kingdom to track them. 
 
 The NATO statement reported that those two Russian bombers were en route back to their homeland. 
 
 "Scrambles and intercepts are standard procedure when an unknown aircraft approaches NATO airspace," the NATO release said. "However, such flights pose a potential risk to civil aviation given that the Russian military often do not file flight plans, or use their on-board transponders." 
 
 Four other Russian aircraft -- two fighter jets and two bombers -- were spotted flying over the Black Sea, prompting Turkish Air Force jets to scramble to track them. 
 
 There were at least seven other Russian planes intercepted over the Baltic Sea today, as well, though NATO would not indicate exactly how many. Baltic Air Policing Mission planes were sent into the air and the Russian aircraft headed back to their own airspace. 
 
 Russian officials have not yet reacted to the NATO report. 
 
 The nearly 20 intercepts came after seven other Russian jets were intercepted over the Baltic Sea on Tuesday. ||||| BRUSSELS NATO aircraft tracked Russian strategic bombers over the Atlantic and Black Sea on Wednesday and sorties of fighters over the Baltic in what the Western alliance called an unusual burst of activity at a tense time in East-West relations. 
 
 In all, NATO said in a statement, its jets had intercepted four groups of Russian aircraft in about 24 hours since Tuesday, and some were still on maneuvers late on Wednesday afternoon. 
 
 "These sizeable Russian flights represent an unusual level of air activity over European airspace," the alliance said. 
 
 A spokesman stressed there had been no violation of NATO airspace -- as there was last week when a Russian spy plane briefly crossed Estonia's border. But such high numbers of sorties in one day were, he said, rare in recent years. 
 
 In the biggest exercise, four Tupolev Tu-95 strategic bombers, a Cold War icon since the 1950s equivalent to the U.S. B-52, flew out over the Norwegian Sea in the early hours of Wednesday, accompanied by four refueling tanker aircraft. 
 
 Norwegian F-16s were scrambled and tracked the formation, which eventually broke up, with six planes heading back toward Russia and two Tu-95s flying on south over the North Sea, where they were intercepted by British Typhoons. Portuguese F-16s later tracked them in the Atlantic before they turned for home. 
 
 A Norwegian military spokesman said: "We see Russian aircraft near our airspace on a regular basis but what was unusual is that it was a large number of aircraft and pushed further south than we normally see." 
 
 In a second incident, two Tu-95s accompanied by two fighter jets were being tracked by Turkish aircraft over the Black Sea on Wednesday afternoon, while flights of seven Russian warplanes were monitored on Tuesday and Wednesday over the Baltic Sea. 
 
 On Tuesday, German and Danish planes were involved in tracking them as well as aircraft from non-NATO states Sweden and Finland. On Wednesday, Portuguese F-16s posted in the Baltic intercepted a similar group of fighters and fighter-bombers. 
 
 NATO said it had conducted more than 100 such intercepts of Russian aircraft this year so far, about three times as many as in 2013, before the confrontation with Moscow over separatist revolts in ex-Soviet Ukraine soured relations. 
 
 President Vladimir Putin has committed to reinvigorating Russia's armed forces, which had been undermined by the economic troubles that followed the collapse of the Soviet Union. Tension over Ukraine has seen the U.S.-led NATO alliance step up its vigilance, especially on its eastern frontiers with Russia. 
 
 The spokesman said there was no particular reason for concern over Russian warplanes exercising their right to fly in international airspace but that such sorties were shadowed by NATO aircraft as a precaution and to protect civil air traffic. 
 
 (Additional reporting by Balazs Koranyi in Oslo; editing by Andrew Roche)
– It's not clear what Vladimir Putin might be up to, but reports of a possible Russian sub spotted off Sweden are now followed by those of NATO, which says it yesterday intercepted at least 19 Russian fighter jets and bombers flying in three separate directions outside Russian airspace. Eight of the planes flew in formation from Russian airspace toward the Norwegian Sea, ABC News reports. Six turned back when intercepted by Norwegian air force F-16s, but two bombers continued on above Norway's coast to the Atlantic Ocean. They were eventually intercepted by British planes and tracked by F-16s from Portugal, Reuters reports. Four Russian planes over the Black Sea were tracked by Turkish air force jets, while at least seven other planes were intercepted over the Baltic Sea for the second day in a row yesterday. While the planes didn't violate NATO airspace, the flights "represent an unusual level of air activity over European airspace" and "such flights pose a potential risk to civil aviation given that the Russian military often do not file flight plans, or use their on-board transponders," says NATO, which has performed more than 100 intercepts of Russian aircraft this year—three times more than in 2013. "We see Russian aircraft near our airspace on a regular basis, but what was unusual is that it was a large number of aircraft and pushed further south than we normally see," a Norwegian military rep adds. A NATO official tells CNN the flights may indicate the start of unannounced Russian air exercises. (Russia is also suspected of hacking the White House.)