By Hyunsu Yim and Hyonhee Shin
SEOUL (Reuters) - South Korea's foreign ministry summoned the Russian ambassador in Seoul on Monday to protest over what it has called the sending of North Korean troops to Russia for deployment in Ukraine.
The Kremlin declined to directly answer a query on whether North Korean troops were going to fight in Ukraine but spokesman Dmitry Peskov said Moscow's cooperation with Pyongyang was not directed against third countries.
South Korea's first vice foreign minister Kim Hong-kyun called in Russian ambassador Georgy Zinoviev and urged the immediate withdrawal of North Korean soldiers from Russia, the ministry said in a statement.
The Kremlin has previously dismissed South Korean assertions that North Korea may have sent some military personnel to help Russia against Ukraine.
Kim said the participation of North Korean troops in the war in Ukraine violated U.N. resolutions and the U.N. charter and posed serious threats to the security of South Korea and beyond.
"We condemn North Korea's illegal military cooperation, including its dispatch of troops to Russia, in the strongest terms," the ministry quoted Kim as saying.
"We will respond jointly with the international community by mobilising all available means against acts that threaten our core security interests."
Zinoviev told Kim that cooperation between Moscow and Pyongyang was in line with international law and was not directed against the security interests of South Korea, the Russian embassy said in a Facebook (NASDAQ:META) post.
South Korea's spy agency said last week that North Korea had shipped 1,500 special forces troops to Russia's Far East for training and acclimatising at local military bases and that they were likely to be deployed for combat in the war in Ukraine.
Ukraine's President Volodymyr Zelenskiy has accused Pyongyang of preparing to send 10,000 soldiers to Russia, and on Sunday called for strong reaction from countries.
'DANGEROUS DEVELOPMENT'
The United States said on Friday it could not confirm reports that North Korean troops were fighting but said that if true, it would be a "dangerous development" in Russia's war against Ukraine.
South Korea's defence ministry said on Monday that Seoul had consulted Washington ahead of the spy agency's announcement, and condemned what it called the North's illegal involvement in Ukraine and urged an immediate halt.
NATO chief Mark Rutte, after a phone call on Monday with South Korean President Yoon Suk Yeol, said on social media platform X that if North Korea were to send troops to Ukraine to fight on Russia's behalf it would significantly escalate the conflict.
Yoon's office said he agreed with Rutte's suggestion for Seoul to send a government delegation to NATO to share more information about North Korea's moves.
Lin Jian, a Chinese foreign ministry spokesperson, said Beijing hoped that all parties would work to de-escalate the situation.
Both Russia and North Korea have denied arms transfers but have pledged to boost military ties, signing a mutual defence treaty at a summit in June.