Russia launched a large-scale missile and drone attack on Ukraine early Monday, killing at least 21 people, including 15 in Kyiv, and injuring dozens.

The assault highlighted growing weaknesses in Ukraine’s air defenses, as all of Russia’s ballistic missiles reportedly reached their targets.

Ukrainian President Volodymyr Zelenskyy is expected to urge allies for more U.S.-made Patriot missile interceptors at this week’s NATO summit.

Russia said the strikes were retaliation for recent Ukrainian long-range attacks on its territory, the AP has reported.

While Ukraine has gained an advantage with drone warfare, shortages of Patriot missiles have left it more vulnerable to Russia’s ballistic missile attacks.