Jens Stoltenberg made the statement following a meeting of the NATO-Ukraine Council in Brussels on Wednesday.
The body met at an ambassadorial level at Ukraine's request, following the recent wave of Russian missile attacks on the country's civilians and infrastructure, according to officials.
Stoltenberg said afterwards: "NATO strongly condemns Russian missile and drone attacks on Ukrainian civilians, including with weapons from North Korea and Iran."
The NATO chief added: "As Moscow intensifies its strikes on Ukrainian cities and civilians, NATO Allies are boosting Ukraine’s air defences. We will continue to stand by the brave Ukrainians as they push back against Russia’s war of aggression.”
During Wednesday's meeting, NATO countries "made clear that they will continue to provide Ukraine with major military, economic, and humanitarian assistance," with many allies outlining plans to "provide billions of euros of further capabilities in 2024," the alliance said in a statement.
NATO also noted that recently Germany supplied Ukraine with "Patriot and Skynex air defence systems and additional missiles for IRIS-T air defences," while Britain "is sending around 200 air defence missiles" to support Kyiv's war effort against the Russian invasion.
The NATO-Ukraine Council was created at the alliance's Vilnius summit in July 2023 and serves as a "forum for joint consultations, decision-making and activities between NATO and Ukraine," according to officials.
Wednesday is day 686 of Russia’s war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
Source: NATO, Reuters