At least 100 North Korean soldiers have been killed in fighting in the Ukraine war since entering combat on the Russian side earlier this month, a South Korean MP has said.

Lee Sung-kwon, speaking to reporters after parliament was briefed by the country's National Intelligence Service, said another 1,000 had been injured.

He said the casualties included high-ranking officials, and could be explained by the troops lack of familiarity with the terrain, and with drone warfare.

The first reports of North Korean casualties came earlier this week. It emerged in October that the North had sent 10,000 troops to help Russia's war effort.

On Monday a US Pentagon spokesman said North Koreans had been killed, without giving a number, and a day later an unnamed US official said that there had been "several hundred" killed or wounded.

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.

The casualties are thought to have occurred in Russia's Kursk region, where Ukrainians are defending a small area of territory captured during a surprise incursion in August.

Last Saturday, Ukrainian President Volodymyr Zelensky said Russia had begun to use a "significant number" of North Koreans in its assaults in Kursk.

They are not thought to have been deployed in Ukraine itself, where Russian troops have been advancing in eastern parts of the country in recent months.

Lee Sung-kwon said there were reports of preparations for additional deployment, and that North Korean leader Kim Jong-un could oversee training.

He quoted intelligence officials as saying the high number of casualties could be attributed to an "unfamiliar battlefield environment, where North Korean forces are being utilised as expendable frontline assault units, and their lack of capability to counter drone attacks".

"Within the Russian military, complaints have reportedly surfaced that the North Korean troops, due to their lack of knowledge about drones, are more of a burden than an asset," he added.

Neither Russia nor the North have acknowledged the troop deployments, but a North Korean statement on Thursday carried by state news agency KCNA said the country's alliance with Moscow was "deterring the US and the West's ill-intended extension of influence".