Russia is preparing to deploy 10,000 additional North Korean troops on top of the existing 8,000 fighting in Vladimir Putin’s war on Ukraine, said Ukrainian president Volodymyr Zelensky.

Citing “new data”, Mr Zelensky said in ​a post on X North Koreans were “being selected for ​training and subsequent deployment to Russia”.

In a latest presidential decree on Monday, the Russian president ordered increasing the size of the army to 1.55 million active servicemen. The number of uniformed personnel will increase by 15,500, while raising the strength of the armed force to 2.4 million, according to the decree.

While the decree does not give a reason for the increase in troop size, it comes as both sides suffer mounting casualties in the war. It also instructed the Russian government to allocate funds to the Ministry of Defence to carry out the increase.

This marks the fourth increase in the military’s authorised strength in seven months after March, June and July, reported Russian and English-language news website Meduza. According to the outlet, together, the four increases added 52,500 defence personnel including, 50,500 service members.

Earlier last year, Mr Putin and North Korean leader Kim Jong Un had confirmed for the first time that North Korean troops were sent to Russia to fight the war in Ukraine, with both the leaders referring to them as “heroes”.

North Korea ​has sent ⁠an estimated 14,000 to 15,000 troops to support Russia’s war in Ukraine since 2024, according to ​Ukrainian and South Korean estimates, with most deployed ​in ⁠the Kursk region to help repel a Ukrainian incursion.

Pyongyang has also supplied Russia with millions of artillery and mortar rounds, ⁠as ​well as ballistic missiles, long-range artillery ​systems and multiple-launch rocket systems, according to Ukrainian and independent assessments.

In August, the Ukrainian president said up to 50,000 North Korean troops could be sent to fight for Russia as he called on South Korea to provide aerial support.

South Korea announced in July a $100m aid package for Ukraine, although it excluded lethal weapons. Seoul also pledged continued humanitarian assistance and support for reconstruction.

Mr Zelensky’s comments on Monday came after ​Seoul and Kyiv were at odds over his announcement last ​week that Ukraine had transferred two captured North Korean soldiers to South ‌Korea.

South Korea ‌demanded an apology from Ukraine after Mr Zelensky disclosed the transfer at the ​UN General Assembly last week, saying Kyiv had breached an agreement to keep it confidential. Seoul said confidentiality was necessary to protect the soldiers and relatives in North Korea, while Kyiv said no secrecy agreement existed.

The move raised questions over how they will be investigated, protested and resettled, along with the legal basis of their transfer.

The soldiers are expected to undergo questioning and security screening before the South Korean authorities decide whether to grant them protection and begin the resettlement process.

Seoul’s Unification Ministry said on Monday their cases would be reviewed under relevant laws and past practices, suggesting that the North Korean Defectors Protection and Settlement ⁠Support Act would apply.