North Korean troops have been killed fighting Ukrainian forces in Russia's Kursk border region, the US has said.

These would be the first reported casualties since it emerged in October that North Korea had sent around 10,000 troops to reinforce Russia's war effort.

Ukraine's military intelligence agency, the GUR, has also said at least 30 North Korean troops had been killed or wounded in fighting over the weekend.

The BBC has not independently verified the claims.

The North Korean troops, none of whom will have any previous combat experience, are believed to have spent their first weeks in Russia in training and then in support roles.

On Saturday, Ukrainian President Volodymyr Zelensky said Russian had begun to use a "significant number" in its assaults in Kursk, part of which Ukraine has occupied since launching a surprise incursion in August.

Speaking to reporters on Monday, Pentagon press secretary Major General Pat Ryder said the US believed North Korean soldiers had "engaged in combat in Kursk alongside Russian forces" and "suffered casualties, both killed and wounded".

He did not give specific numbers, but said the troops had been in combat since "a little over a week ago".

He added it appeared the North Koreans were being used in infantry roles and that their involvement was thought so far to be limited to Kursk, implying that they have not been deployed in Ukraine itself.

Russian forces, who launched a full-scale invasion of Ukraine in February 2022, have been advancing in eastern parts of the country in recent months.

The GUR said the North Korean casualties had occurred on Saturday and Sunday in the Kursk villages of Plekhovo, Vorobzha, and Martynovka.

On Monday, President Zelensky posted drone footage on Telegram that showed a number of men taking cover behind trees, saying they were North Korean troops who had just taken part in an assault on a Ukrainian position.

He also posted footage which he said showed Russian troops trying to conceal the presence of North Koreans on the battlefield by using a campfire to burn the faces of those who had been killed.

"Ukraine's Defense Forces and intelligence are working to determine the full extent of the actual losses suffered by Russian units that include North Koreans," he said.

He added that there was "not a single reason for North Koreans to die in this war".

The Kremlin referred questions about North Korean deaths to the Russian Ministry of Defence, which has made no comment.

Following reports of the deaths, the EU and countries including the UK, US, Australia and South Korea called Pyongyang's involvement in the conflict a "dangerous expansion... with serious consequences for European and Indo-Pacific security."

Earlier this week, the US Treasury department announced sanctions on nine people and seven entities over their financial and military support to North Korea.