South Korea’s national defense minister on Tuesday said North Korean troops appear to have been killed or wounded in Russia’s war on Ukraine.

Minister of National Defense Kim Yong-hyun told lawmakers on this day that reports of North Korean troop casualties in the Ukraine war are believed to be true based on the ministry’s findings.

He was speaking about a report in the Ukrainian news agency Kyiv Post that six North Korean officers were among those killed by a missile strike in a Russian-occupied area near Donetsk in eastern Ukraine on Friday.

“We believe there have been some North Korean troop fatalities and injuries in Ukraine,” he said.

The defense minister added he believes North Korea could send more of its troops to Ukraine in the future.

“The matter of North Korea dispatching troops to aid Russia is also highly likely,” he said, citing the mutual defense pact reached between the two countries during Russian President Vladimir Putin’s visit to Pyongyang in June.

“The relations between Russia and North Korea are evolving to be almost as close as a military alliance,” he said. “As such more North Korean troops could be deployed to Ukraine, from how we look at it.”

North Korea advancing its nuclear and missile capabilities has posed serious threats to the security situation in the Korean Peninsula and elsewhere, to which South Korea has responded with a “nuclear-based alliance with the US,” he said.

The minister said North Korea’s capacity to build a nuclear-powered submarine, mentioned by its leader Kim Jong-un last month, was “limited” and “in the early stages.”

The South Korean military is looking into the possibility the recent activities detected around Sinpo, the North Korean port city where its submarine base is located, are linked to the new nuclear submarine hinted at by its leader Kim. In January, North Korea test-launched its cruise missiles, fired from near Sinpo.

The defense minister said the North Korean claims of its military reconnaissance satellite having taken images of the US nuclear submarine that arrived in Busan last month were also likely false.

“North Korea’s military reconnaissance satellite technology is quite crass. It would not have been able to identify the US submarine,” he said.

The South Korean military was still assessing the credibility of North Korean claims related to its new ballistic missiles with “super-large” warheads and first hypersonic missiles, he added.