North Korean forces have suffered “several hundred” casualties fighting against Ukrainian troops in Russia’s Kursk region, according to a senior US military official.

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, using an abbreviation for North Korea’s official name.

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

“These are not battle-hardened troops. They haven’t been in combat before,” the official said, adding that this was probably contributing to “why they have been suffering the casualties that they have at the hands of the Ukrainians”.

The official’s comments on casualties 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.

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

Experts say the nuclear-armed North’s leader, Kim Jong-un, is keen to acquire advanced technology from Russia and battle experience for his troops.

US President Joe Biden’s administration has been a key supporter of Kyiv, and has been rushing to provide it with billions of dollars in already authorised aid before president-elect Donald Trump takes office next month.

Trump has repeatedly criticised US assistance for Ukraine and claimed he could secure a ceasefire within hours – comments that have triggered fears in Kyiv and Europe about the future of US aid under his administration.

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

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