Ukraine has been hit by a surge in Russian ballistic missile attacks, about a third of which used North Korean weapons that can only fly because they run on Western circuitry, obtained despite sanctions,

Pyongyang has long coveted an advanced air-defense system to guard against missiles and war planes from the United States and South Korea.

The South Korean assessment came after Russia warned Monday that President Joe Biden’s decision to let Ukraine strike targets inside Russia with U.S.-supplied longer-range missiles adds “fuel to the fire” of the war.