U.S. President Joe Biden said Kyiv should strike back at North Korean troops "if they go into Ukraine" during a press conference on Oct. 29.
A Pentagon spokesman added at a separate briefing that Moscow’s recourse to North Korean troops reflects a "dire situation" of its manpower.
North Korea had sent troops to Russia to participate in its war against Ukraine, NATO Secretary General Mark Rutte confirmed on Oct. 28. U.S. intelligence estimated the number of troops to be around 10,000, part of whom is already deployed in Russia's Kursk Oblast.
"I am concerned about it, yes," Biden answered to a question regarding their arrival, adding that Ukraine should strike back if the troops enter into Ukrainian territory, but did not elaborate further.
In a separate news briefing on Oct. 28, Pentagon spokesperson Major General Pat Ryder said a "relatively small number" of North Korean troops are already in Kursk Oblast, echoing recent comments by Defense Secretary Lloyd Austin, who said thousands more troops are expected to head there in the coming weeks.
A South Korean delegation will visit Ukraine in the second part of the week to share information on North Korea's troops in Russia and discuss cooperation.
North Korea’s entry into the war comes when Russia's long and grinding campaign in Ukraine's eastern Donbas region has dramatically gained pace in recent days, with analysts saying Moscow's forces are advancing at a pace not seen since the early months of the war.