"It has been Russia that has escalated the conflict time and time again," spokesperson Miller said, pointing to North Korean troops the US says have been deployed and clashed with Ukrainian forces.
Russian and/or North Korean threats of support for Iran could lay the groundwork for a multi-state nuclear conflict, one that could come to involve the United States and/or China.
US authorities previously reported the presence of around 10,000 North Korean soldiers in western Russia's Kursk region, but Zelensky confirmed combat involvement.
Zelensky: North Korean troops threaten Ukraine as the world passively watches.
"The US strategic nuclear means pose an "ever-increasing threat" to North Korea's security environment," Kim Jong Un was reported as saying.
South Korea will respond to the North's activities with all available means, it added, without elaborating on what actions it might take.
We may not be heading for a world war, but we could be heading for a world at war. Here's a look at the big conflicts around the world, and ones that could soon erupt, with nuclear-armed nations.
The South Korean military spokesperson warned that North Korea was making preparations to blow up the border as soon as Monday.
North Korea is providing up to half of the artillery shells used by Russia in Ukraine. Experts warn of growing cooperation, including potential transfers of advanced weapons systems.
Israel should clarify its nuclear stance and take action against Iran while it’s not yet nuclear to maintain its strategic advantage.