SEOUL, Oct 18, 2024 (BSS/AFP) - North Korea has decided to send "large-scale troops" to support Russia in its war against Ukraine, South Korea's Yonhap news agency reported Friday, citing Seoul's spy agency.

"The National Intelligence Service said it has learned that the North has recently decided to send four brigades of 12,000 soldiers, including special forces, to the war in Ukraine," Yonhap said.

The NIS declined to confirm the report to AFP.

"The movement of North Korean troops has already begun," an NIS source told Yonhap.

Ukrainian President Volodymyr Zelensky said Thursday he had intelligence reports that North Korea was training 10,000 soldiers to support Russia in its fight against Kyiv.

"They are preparing on their land, 10,000 soldiers, but they didn't move them already to Ukraine or to Russia," Zelensky said after meeting NATO defence ministers.

Zelensky suggested that Russia is relying on North Korean troops to compensate for its substantial losses, as many young Russians seek to avoid conscription.

South Korea's President Yoon Suk Yeol convened an emergency security meeting Friday on the move by Pyongyang.

The meeting said that the close military ties between Russia and North Korea had gone "beyond the transfer of military supplies to actual troop deployments".

This development poses "a significant security threat not only to our country but also to the international community," the president's office said in a statement.

Pyongyang and Moscow have been allies since North Korea's founding after World War II and have drawn even closer since Russia's 2022 invasion of Ukraine, with Seoul and Washington long claiming that Kim Jong Un has been sending weapons for use in Ukraine.

Russian President Vladimir Putin made a rare visit to Pyongyang in June, with the two countries signing a mutual defence treaty, fuelling speculations of further arms transfers -- which violate rafts of UN sanctions on both countries.

Earlier this month, Ukrainian media reported that six North Korean military officers were killed in a Ukrainian missile attack on Russian-occupied territory near Donetsk on October 3.

Seoul's defence minister, Kim Yong-hyun, told lawmakers at the time that it was "highly likely" that the report was true.

Experts said that moving from supplying shells to soldiers to Russia was the logical next step.

"For North Korea, which has supplied Russia with many shells and missiles, it's crucial to learn how to handle different weapons and gain real-world combat experience," said Lim Eul-chul, a professor at Seoul's Institute for Far Eastern Studies.

"This might even be a driving factor behind sending North Korean soldiers -- to provide them with diverse experiences and war-time training," he told AFP.