Washington DC - The US and South Korean defense chiefs called Wednesday for North Korea to withdraw its troops from Russia, where Washington says some 10,000 of them have been deployed for possible use against Ukrainian forces.

"I call upon them to withdraw their troops out of Russia," US Defense Secretary Lloyd Austin said at the Pentagon, speaking alongside his South Korean counterpart Kim Yong-hyun, who urged the "immediate withdrawal" of Pyongyang's forces.

Austin said the US will "continue to work with allies and partners to discourage Russia from employing these troops in combat," but warned Moscow is likely to do so.

The Pentagon said the previous day that a "small number" of North Korean troops have already been deployed in Russia's Kursk region, where Ukrainian troops have been conducting a ground offensive since August.

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Experts have said that in return for these forces, North Korea is likely aiming to acquire military technology, ranging from surveillance satellites to submarines, plus possible security guarantees from Moscow.

Russia and North Korea have boosted their political and military alliance over the course of the Ukraine conflict. Both are under sanctions – Pyongyang for its nuclear weapons program, and Moscow for its war against Kyiv.