Kursk, Russia - North Korean forces have suffered "several hundred" casualties fighting against Ukrainian troops in Russia's Kursk region, a senior US military official claimed Tuesday.

Pyongyang has sent thousands of troops to reinforce Russia's war effort, including to the Kursk border region, where Ukrainian forces seized territory earlier this year.

"Several hundred casualties is our latest estimate that the DPRK has suffered," the official said on condition of anonymity.

This "would include everything from... light wounds up to being KIA (killed in action)," the official claimed, with soldiers of "all ranks" among the casualties.

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"These are not battle-hardened troops. They haven't been in combat before," the official said, which explains "why they have been suffering the casualties that they have at the hands of the Ukrainians."

The comments, echoing similar statements made by Ukrainian officials, came after Ukraine's commander-in-chief Oleksandr Syrsky said Russia has used North Korean troops at the heart of an "intensive offensive" in Kursk over several days. Ukrainian President Volodymyr Zelensky also posted footage on X claiming to show North Korean soldiers on the battlefield.

North Korea and Russia have strengthened their military ties since Moscow's invasion of Ukraine in February 2022. A landmark defense pact between Pyongyang and Moscow signed in June came into force earlier this month.

Meanwhile, outgoing US President Joe Biden's administration has been rushing to provide Ukraine with billions of dollars in already authorized aid before Donald Trump takes office next month.

Trump has repeatedly criticized US assistance to Ukraine and claimed he could secure a ceasefire within hours, which has triggered fears about the future of US aid.

A senior defense official said Tuesday that not all of the remaining $5.6 billion that can be drawn from US stocks may be used in time.

"I would certainly anticipate that... there could be remaining authority that would transition and be available for the next administration to use," the official said on condition of anonymity.