- The comments were made by the head of Ukraine's military intelligence agency GUR.
- "They supply huge amounts of artillery ammunition, which is critical for Russia," said Kyrylo Budanov.
In the wake of the Ukraine war, Russia has formed a close alliance with China, the world's second-biggest economy, and boosted trade ties with other major economies, such as India.
Yet according to the head of Ukraine's military intelligence agency GUR, Kyrylo Budanov, the Kremlin's most important ally during the war isn't economically and militarily powerful China, but North Korea, an isolated pariah state whose economy has been damaged by decades of sanctions.
Speaking at an event in Kyiv Saturday, Budanov said that North Korea's military aid to Russia was of more concern to Ukraine than the support Russia's other allies had provided, reported Reuters.
"They supply huge amounts of artillery ammunition, which is critical for Russia," he said, pointing to an increase in battlefield hostilities following such deliveries.
For decades, North Korea has been among the poorest and most isolated Asian countries, with the UN imposing severe sanctions to curtail its nuclear weapons program.
However, the Ukraine war enabled North Korean leader Kim Jong Un to improve his situation, forming a valuable security pact with Russian President Vladimir Putin's Russia in June.
As Russia's Ukraine invasion has developed into a grinding war of attrition, both sides are firing huge numbers of shells daily, and replenishing supplies has become a major challenge.
Russia has found a new supply line in North Korea, which has sent millions of shells from its aging stockpiles as well as boosted domestic production to supply the Kremlin's forces.
In return, Kim has secured new security pledges from Putin, alongside access to valuable Russian military technology.
Ukraine's Western allies, meanwhile, have struggled to keep pace with the demand for shells, meaning Russia has secured an important advantage.
North Korea has also provided Russia with ballistic missiles, that the US Defense Intelligence Agency in May said had been used by Russia in attacks on Ukrainian towns.
According to reports, North Korean shells and other equipment are often of dubious quality, but they remain an important resource for the Russian military, analysts told Business Insider in August.
Russia has also secured supplies of ballistic missiles from Iran in recent weeks, and Budanov reportedly said it was also boosting its capacity to produce the "glide bomb" missiles that devastated Ukrainian positions.
Ukraine is currently battling to hold back intensifying Russian attacks in Donetsk, east Ukraine, but has seized control of a swath of Russian territory in Kursk.