CNN
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North Korea is sending its citizens to support the Russian military in the fight against Ukraine, Volodymyr Zelensky said, increasing concerns about the alliance between Moscow and the secretive state.

In his daily video message on Sunday, the Ukrainian president said: “We see a growing alliance between Russia and regimes like North Korea. It's no longer just about arms transfers. It’s actually about handing over people from North Korea to the occupying forces.”

Zelensky's accusation comes against the backdrop of increasingly friendly relations between Moscow and Pyongyang. Russian President Vladimir Putin visited North Korea in June – the first such visit in more than two decades – and Western observers questioned how much North Korea supported Russia's invasion of Ukraine.

“Of course, in such circumstances, our relationships with our partners need to be strengthened. “The front needs more support,” Zelensky added, repeating his request for Western nations to allow Kiev to use long-range missiles on Russian territory.

A Ukrainian intelligence source, who did not want to be named because of the sensitivity of the issue, told CNN last week that a small number of North Koreans have been working with the Russian military, mostly to help with technology and share information about the use of North Korean munitions . Some of them were recently killed in eastern Ukraine, the source said.

Kremlin spokesman Dmitry Peskov on Thursday dismissed allegations that North Korean personnel had been sent to Russia to help as “another hoax.”

But South Korea's National Intelligence Service said last week it was monitoring developments and believed the claim could be accurate.

Defense Minister Kim Yong-hyun said at the annual parliamentary audit of the defense sector on Tuesday that it was “highly likely that the reported losses of North Korean officers and soldiers in Ukraine are true under various circumstances.”

“We believe that the possibility of further deployment of regular troops is very high, since Russia and North Korea have concluded a mutual agreement that is almost tantamount to a military alliance. We will also be well prepared for this possibility,” he added.

Several governments have accused Pyongyang of supplying Moscow with weapons because of its bitter war in Ukraine. Both countries denied this allegation, despite considerable evidence of such transfers.

The two nations, both pariahs in the West, have forged increasingly friendly relations since Russia's invasion.

During Putin's visit to the North Korean capital in June, the two countries pledged to use all available means to provide immediate military assistance in the event of an attack on the other country. This is part of a groundbreaking defense pact agreed upon by the autocratic nations.

Putin said during that trip that the two countries would expand their relations to a “new level.”

In remarks ahead of the talks between the two, North Korean leader Kim Jong Un expressed his “full support and solidarity with the struggles of the Russian government, military and people,” and particularly referred to Moscow's war in Ukraine “for its… to protect our own sovereignty, security and territorial stability.”