South Korea has summoned the Russian ambassador, seeking the "immediate withdrawal" of North Korean troops which it says are being trained to combat successful Ukraine.
About 1,500 North Korean soldiers, including those from the peculiar forces, person already arrived successful Russia, according to Seoul's spy agency.
In a gathering with the ambassador Georgiy Zinoviev, South Korea's vice-foreign curate Kim Hong-kyun denounced the determination and warned that Seoul volition "respond with each measures available".
Mr Zinoviev said helium would relay the concerns, but stressed that the practice betwixt Moscow and Pyongyang is "within the model of planetary law".
It is unclear what practice helium was referring to. The ambassador did not corroborate allegations that North Korea has sent troops to combat with Russia's military.
Pyongyang has besides not commented connected the allegations.
South Korea has agelong accused the North of supplying weapons to Russia for usage successful the warfare against Ukraine, but it says the existent concern has gone beyond the transportation of subject materials.
Some South Korean media reports person suggested arsenic galore as12,000 North Korean soldiers are expected to beryllium deployed.
"[This] not lone gravely threatens South Korea but the planetary community," Kim said connected Monday.
Moscow and Pyongyang person stepped up practice aft their leaders Vladimir Putin and Kim Jong Un signed a information pact successful June, volition pledges that their countries volition assistance each different successful the lawsuit of "aggression" against either country.
Last week, Putin introduced a measure to ratify the pact.
Pyongyang's deployment of troops to combat with Russia "would people a important escalation" successful the conflict, Nato secretary-general Mark Rutte said connected Monday.
The United States and Japan person besides condemned the deepening subject ties betwixt North Korea and Russia.
Some defence experts told BBC Korean that North Korea's engagement could complicate the war.
"North Korea’s engagement could unfastened the doorway for greater planetary information successful the conflict, perchance drafting successful much countries," said Moon Seong-mok from the Korea National Strategy Institute.
"The planetary assemblage volition apt summation sanctions and unit connected some Russia and North Korea, but it remains to beryllium seen whether North Korea’s engagement volition genuinely payment either country," Dr Moon said.
But others judge the Russian subject units volition person difficulties incorporating North Korean troops into their frontlines.
Apart from the connection barrier, the North Korean service has nary caller combat experiences, they said.
Valeriy Ryabykh, exertion of the Ukrainian work Defence Express, said the North Korean soldiers could beryllium asked to defender sections of the Russian-Ukrainian border, which volition escaped up Russian units to combat elsewhere.
"I would regularisation retired the anticipation that these units volition instantly look connected the beforehand line," helium said.
Additional reporting by Sangmi Han, Jake Kwon and Hosu Lee successful Seoul