SEOUL — North Korean soldiers are supporting Russian troops on the ground, and some may have already been killed and injured, South Korean and Ukrainian officials said this week, raising questions about whether the military cooperation between Pyongyang and Moscow has advanced to a new stage.

A Ukrainian military intelligence official, speaking on the condition of anonymity to discuss a sensitive security matter, said “several thousand” North Korean infantry soldiers are undergoing training in Russia now and could be deployed to the front line in Ukraine by the end of this year.

The official said North Korean officers are already on the ground in Russia-occupied Ukraine to observe Russian forces and study the battlefield, but Kyiv hasn’t seen any North Korean units fighting yet.

Kremlin spokesman Dmitry Peskov on Thursday dismissed claims of Pyongyang sending military personnel to fight in Ukraine as a “hoax.”

Reports of North Korean soldiers supporting Russians in the Russia-occupied territory of Donbas surfaced on Telegram channels and in the Ukrainian press last week.

This comes after North Korean leader Kim Jong Un and Russian President Vladimir Putin signed a mutual defense pact this summer, with Kim pledging “full” support for Putin in his fight against Ukraine.

The pact underscored the way the outcast leaders of these two heavily sanctioned states have deepened their partnership against a Western-led global order since Putin’s invasion of Ukraine at the start of 2022.

Moscow first turned to Pyongyang for weapons support. The United States says North Korea has sent large amounts of munitions, including artillery shells, to Russia. Both North Korea and Russia have denied the allegations.

Now, apparently, Pyongyang is sending soldiers.

South Korean Defense Minister Kim Yong-hyun called the reports of North Korean troops helping Russians “highly likely” during a National Assembly meeting on Tuesday, adding that Seoul expects Pyongyang to send more personnel to support Russia’s war effort.

“Russia and North Korea have an agreement that is basically a military alliance, so it is highly likely that North Korea would send additional troops,” Kim told lawmakers. “That’s how we’re assessing it, and we will definitely prepare for it.”

Ukraine claims that Pyongyang sent military personnel to supervise the use of North Korean ammunition and ballistic missiles, and some have been killed in the line of fire.

Andriy Kovalenko, the head of Ukraine’s Center for Countering Disinformation, which is a part of the national security and defense council, posted on Telegram later on Tuesday saying that Pyongyang had already sent troops, including military engineers supervising the use of weapons, and “some have already died.”

The Ukrainian military intelligence official said that it’s unclear where the combat units that are training in Russia would be deployed on the Ukraine front. Moscow could use them in Russian border regions, freeing up Russian troops to fight in Ukraine, the official said.

“It could have a significant impact. Especially if we’re talking about freeing up reserves within the territory of the Russian Federation itself,” the official said.

Some South Korean experts say it’s a feasible scenario.

In 2022, the two nations appeared to discuss the possibility of North Korean laborers being sent to Russia-occupied eastern Ukraine to help with reconstruction efforts. Russian officials publicly welcomed the prospect of North Korean laborers, and some workers appear to have been dispatched to Ukraine’s Donbas region, reported Daily NK, a Seoul-based monitoring group with informants inside North Korea. Citing unnamed sources in North Korea and Russia, Daily NK reported in April that Pyongyang sent about 150 new laborers there to help with rebuilding efforts.

North Korea has a long history of sending workers — mainly lumberjacks and builders — to Russia to earn money for the cash-strapped regime, despite a United Nations prohibition on governments issuing new work permits to North Koreans.

While weapons from Pyongyang are based on old Soviet-era technology, North Koreans have made modifications that would require in-person guidance and supervision, said Cha Du-hyeogn, a former South Korean intelligence adviser who is now a North Korea analyst at the Asan Institute for Policy Studies in Seoul.

“The front line is where these weapons are being used, so of course North Koreans would supervise their use on the front line, rather than from Moscow,” Cha said.

Cha added that the presence of technical advisers could be a sign that Pyongyang is not only providing artillery shells that can be easily inserted into Russian weapons, but also more advanced weapons such as armored vehicles, missiles and multiple rocket launchers that need in-person guidance.

Reports of North Koreans on the front lines began circulating when an anonymous Russian Telegram channel, the Kremlin Snuffbox, posted that a Ukrainian missile strike on the Russian-occupied territory of Donetsk killed more than 20 soldiers, including six North Korean military officers.

Citing Russian defense ministry sources, it claimed that three other North Koreans were injured and that the North Koreans had arrived on an “exchange of experience” on the front lines. The Ukrainian military official confirmed that the Oct. 3 Ukrainian missile strike resulted in the death of North Korean officers who “did not directly participate in combat, but they were military personnel already integrated” with Russian forces.

Although foreign intervention by North Korea is rare, it has previously sent military personnel to help with weapons use and technology. In 2016, North Korean missile technicians traveled to Damascus and reportedly stayed at Syrian military facilities, and helped operate chemical and missile factories in Barzah, Adra and Hama, according to the U.N. Panel of Experts that had monitored North Korea’s sanctions-busting activities.

North Korea also used military assistance, including weapons and training, to strengthen bilateral relations with other developing countries, including in Africa. And during the Vietnam War, North Korea sent pilots to help defend North Vietnam against U.S. air attacks, according to Vietnamese records.

Khudov and Khurshudyan reported from Kyiv. Natalia Abbakumova in Riga, Latvia, contributed to this report.

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• North Korean troops ‘highly likely’ to be fighting for Russia in Ukraine, defense chief says