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. 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. "These sizable Russian flights represent an unusual level of air activity over European airspace," NATO said in a statement released this afternoon. 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. 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. 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. 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. 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. 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. 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.
– 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.)