NATO is going to try and use this as justification for sending bombers to the borders of Ukraine to establish 'no fly zones' in effect.
Ukrainian General Staff: The bombing of Kharkiv was carried out from the Russian Tu-22m3 strategic bomber. About 16 high-precision air-to-ground missiles were fired.
The bomber made four attacks on the route Besedina (Kursk region) - Belgorod and fired missiles without crossing the Ukrainian state border.
Needless to say, NATO providing intelligence and EW support already makes them legitimate targets in accordance to the laws on warfare.