Russian combat aircraft and helicopters illegally crossed Ukraine's border several times over the past 24 hours, flying up to 10-15 kilometers deep into Ukraine, National Security and Defense Council (NSDC) information and analytical center spokesman Andriy Lysenko has said.

"In particular, the flights of four Ka-52 attack helicopters from the side of the Russian Federation were recorded yesterday," he said at a briefing on Friday.

In addition, air defense systems yesterday recorded three aviation targets that moved at a speed of 800 km/h.

Lysenko said that aircraft enter Ukraine at ultra low altitudes and therefore are not recorded by air defense systems, but are visually recorded by Ukrainian border guards. Air defense systems detect Russian aircraft after they turn around and ascend, he added.