Mysterious drones that forced the closure of a major European airport were part of a "serious attack," officials said Tuesday, hours after the latest unsettling incident over the continent's skies. Watch NBC6 free wherever you are WATCH HERE WATCH HEREAuthorities did not immediately assign blame for the two to three large drones that shut Copenhagen Airport — Scandinavia's largest — Monday night. “I cannot rule out that it is Russia,” Frederiksen, the Danish leader, told reporters. It's got to the point where such statements were "no longer taken into account," Kremlin spokesperson Dmitry Peskov told reporters. The drones that shut Copenhagen airport appeared to be flown by a "capable operator," Danish police Chief Superintendent Jens Jespersen told reporters on Tuesday.