Ukrainian President Volodymyr Zelenskiy has said up to 50,000 North Korean soldiers ​will be deployed in Russia to ​fight for Pyongyang's ally, while calling on South Korea to provide ​support for its air defence.Zelenskiy said on X on Saturday that "a decision has been made for 30,000 to 50,000 North Koreans to be deployed on the territory of Russia", a higher figure than his estimate of ‌30,000 in ⁠July. He ⁠did not elaborate on how he obtained the information.He said Kyiv had found some North Korean missiles in ​Ukraine's territory, without disclosing their locations."It is absolutely clear that North Korea will continue to build its experience ​in modern warfare, receive licenses from Russia, and receive all kinds of military tools from them," he said.Urging Seoul to have closer cooperation with Kyiv, Zelenskiy said that Ukraine "would very ​much like to receive support from South Korea in an ⁠area where ‌we have a shortage", referring to its air defence systems."We are ​ready to work ​on the Drone Deal and other areas as well," he said, adding ⁠that Ukrainian diplomats "are in contact" with Seoul to push potential ​deals.Russian President Vladimir Putin and North Korean leader Kim signed a ​comprehensive strategic partnership treaty during Putin's June 2024 visit to Pyongyang. The pact includes a mutual assistance provision if either country faces external aggression.North Korea has cast its deployment as assistance to a treaty partner.North Korea has sent so far an estimated 14,000 soldiers to Russia's Kursk Region in 2024, helping Moscow beat back a major incursion into the region ‌by Ukrainian forces.This month, an official at Ukraine's military intelligence told Reuters that a North Korean missile unit has begun deploying to western Russia and ​could be ​equipped with 120 ballistic missiles ⁠and six launchers for strikes against Ukraine.Ukraine is very short of high-end air defences and Russia has tried to exploit this by using more ballistic missiles, which are particularly hard to ​shoot down.North Korea has supplied Russia with millions of artillery and mortar rounds, ballistic missiles, long-range artillery and multiple-launch rocket systems, according to Ukrainian and independent assessments.The North Korean Embassy in Russia did not immediately respond to a request from Reuters for a comment.South Korea's Foreign Ministry did not respond to a request from Reuters for a comment outside business hours.