In some instances, Russian fighter jets have invaded Ukrainian airspace.
National Security and Defense Council spokesman Andriy Lysenko said that the two Russian Armed Forces fighter jets involved in the provocations "periodically take off from a military airfield in Valuyki, Belgorod region."
There was no further information regarding the frequency of the provocative flight paths.
"One of the aircraft," he said, "runs in a westerly direction along the border with Ukraine, the other -- in the east, there are cases of crossing Ukraine's airspace."
The provocative flights have increased recently, Lysenko observed.