North Korean forces have suffered hundreds of casualties in the conflict between Russia and Ukraine, according to estimates by an unnamed US official.

In the Kursk region of Russia, which has been partly occupied by Ukrainian forces, a US official was quoted as saying by news reports Tuesday that "several hundred casualties is our latest estimate that (North Korea) has suffered."

Around 10,000 North Korean troops are believed to have been deployed to engage in combat alongside Russian forces against Ukrainian soldiers.

The official also reportedly said the casualties included North Korean soldiers of all ranks, from lower-level troops to those "very near the top."

The comment came a day after the first indication by US officials about North Korean casualties in the battle, amid speculation that North Korean troops had been reinforcing Russian forces attempting to expel Ukrainian forces from the Kursk region.

US National Security spokesperson John Kirby told reporters Monday that North Korean forces in the Kursk region suffered "significant losses," amounting to "several dozen."

Pentagon spokesperson Maj. Gen. Pat Ryder was also quoted as saying by news reports Monday that Washington "(does) have indications that (North Korean soldiers) have suffered casualties, both killed and wounded."

Ukraine's intelligence agency also indicated Monday that around 30 North Korean troops were killed or wounded in the Kursk region.

While the estimates of North Korean losses by the US authorities have grown significantly in the past couple of days, intelligence authorities or the ministries of the government of South Korea have yet to confirm the information about North Korean casualties as of Wednesday morning. South Korea is currently suffering a leadership vacuum with President Yoon Suk Yeol being suspended from his role for an impeachment trial.

On Tuesday, the National Intelligence Service said it was "corroborating the reports, weighing the possibilities that these revelations are true," adding that it "had obtained related intelligence from various sources" without clarifying further.

North Korea and Russia strengthened military cooperation with the new pact ratified by the two in November, with North Korean leader Kim Jong-un thought to have sought advanced military technology, and battle experience for North Korean troops.