At least 100 North Korean troops deployed to Russia have been killed, with another 1,000 injured in combat against Ukrainian forces in intense fighting in the Kursk region, a South Korean lawmaker said on Thursday, citing the country’s spy agency.

The heavy losses are attributed to the lack of experience by North Korean troops in drone warfare and unfamiliarity with the open terrain where they are taking part in the battle, a member of parliament Lee Seong-kweun told reporters.

Lee was speaking after a closed-door briefing by the National Intelligence Service (NIS) to parliament.

The discrepancy in the estimate of the troops killed from that made by a US military official who cited several hundred casualties is because of the relatively conservative analysis by the NIS, Lee said.

“There was a report that there have been at least 100 deaths and the injured are approaching 1,000,” he said.

There are indications that the North is preparing for additional deployment, Lee said, including intelligence of the country’s leader Kim Jong Un overseeing training.

The report echoed comments by US and Ukrainian officials that North Korean losses are heavy and that Russia was using them in large numbers in assaults in Kursk, a Russian region where Ukraine launched a cross-border incursion in August.

More than 10,000 North Korean troops have been deployed to help Russia in the war, according to US and South Korean officials. Pyongyang has also shipped more than 10,000 containers of artillery rounds, anti-tank rockets, as well as mechanised howitzers and rocket launchers.

Neither the North nor Russia have officially acknowledged the troop deployment or the weapons supply.

Russian President Vladimir Putin visited Pyongyang in June and signed a “comprehensive strategic partnership” treaty with North Korean leader Kim Jong Un that included a mutual defence pact.

Earlier on Thursday, North Korea said its military alliance with Russia is proving “very effective” in deterring the United States and its “vassal forces,” denouncing a recent statement by Washington and allies against ties between Pyongyang and Moscow.

North Korea made no mention of its involvement in the war in Ukraine or casualties.

Instead, it denounced a statement by the United States and nine countries and the European Union issued on Monday as “distorting and slandering the essence of the normal cooperative relations” between the North and Russia.

In a statement by an unnamed foreign ministry spokesman, the North blamed Washington and its allies for prolonging the Ukrainian war and destabilising the security situation in Europe and Asia-Pacific.

“It is because of the misguided acts of the US and the West persisting in their structure-destructive, hegemony-oriented and adventuristic military policy,” it said.