NATO air forces were scrambled more than 300 times in response to Russian military aircraft in 2023, the treaty organization said on Friday.

"The vast majority of aerial encounters between NATO and Russian jets were safe and professional. Breaches of NATO airspace by Russian military aircraft remained rare and generally of short duration," NATO said, adding most intercepts occurred over the Baltic Sea.

Following Russia's invasion of Ukraine in February last year, NATO substantially reinforced its eastern flank air defenses with more fighter jets, surveillance flights and ground-based air defenses.

"NATO fighter jets are on duty around the clock, ready to scramble in case of suspicious or unannounced flights near the airspace of our Allies," NATO spokesperson Dylan White said in a statement.

Earlier on Friday, Russia launched one of its biggest missile attacks on Ukraine of the war so far, killing 12 civilians, wounding dozens more and hitting residential buildings in Kyiv, the south and west of the country.