South Korea’s president said his government “won’t sit idle” as North Korea allegedly sends troops to support Russia’s war on Ukraine, as he met with the leader of Poland to discuss expanding defence cooperation amid the ongoing conflict.

The meeting between South Korean President Yoon Suk Yeol and Polish President Andrzej Duda came a day after US and South Korean officials said they believe around 3,000 North Korean troops have been deployed to Russia and are training at several locations.

South Korea’s spy agency told legislators that North Korea likely aims to send a total of 10,000 troops to Russia by the end of the year.

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South Korean President Yoon Suk Yeol and Poland’s President Andrzej Duda speak during a joint press conference at the Presidential Office in Seoul (Jeon Heon-Kyun/AP)

Both Moscow and Pyongyang have denied the presence of North Korean troops.

“We agreed that North Korea’s troop deployment to Russia, which is in direct violation of the UN charter and UN Security Council resolutions, is a provocation that threatens global security,” Mr Yoon said after the summit.

Mr Yoon said South Korea will work with allies and partners to prepare counter-measures that could be rolled out in stages depending on the degree of military cooperation between Pyongyang and Moscow.

His office said earlier this week that South Korea is considering various diplomatic, economic and military options, including supplying Ukraine with both defensive and offensive weapons systems.

South Korea, a growing arms exporter, has provided humanitarian aid and other non-lethal support to Ukraine and supported US-led economic sanctions against Moscow.

But Seoul has not directly provided Ukraine with arms, citing a long-standing policy of not supplying weapons to countries actively engaged in conflict.

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Polish President Andrzej Duda and his wife Agata Kornhauser-Duda visit the National Cemetery in Seoul, South Korea (Ahn Young-joon/AP)

Tensions on the Korean Peninsula have worsened since 2022 after North Korean leader Kim Jong Un used Russia’s invasion of Ukraine as a distraction to accelerate the growth of his nuclear weapons and missile programme.

Seoul also worries as experts say the North may seek major technology transfers in return for sending troops, including Russian know-how on intercontinental ballistic missiles and submarines that would advance the threat posed by Kim’s nuclear arsenal.

During their summit, Mr Yoon and Mr Duda agreed to “actively support” additional deliveries of South Korean military equipment to Poland, including a new deal for Korean K-2 tanks the governments hope to finalise within this year, Mr Yoon’s office said.

Poland has signed a series of arms deals with South Korea in the last two years to acquire tanks, howitzers and missile launchers in an effort to bolster its military capabilities following Russia’s invasion of Ukraine.