Currently, nearly 11,000 North Korean infantry troops are trained in eastern Russia to fight in Ukraine, Kiev's Defense Intelligence Directorate said.

There have been several reports this week that Moscow plans to use North Korean soldiers to push Ukrainian forces out of Kursk, where they have been invading since August 6.

Lt. Gen. Kyrylo Budanov of Ukraine's Defense Intelligence told The War Zone on Thursday that these battalions will be combat-ready in Ukraine by Nov. 1.

He said North Korean troops would use Russian equipment and ammunition, with the first cadre consisting of 2,600 troops being sent to Kursk.

“We don’t have a complete picture at the moment,” he added.

Hours earlier, Ukrainian President Volodymyr Zelensky told reporters in Brussels that about 10,000 North Korean soldiers were preparing to fight for Russia.

He warned that the involvement of a third nation in the war would be the “first step toward a world war.” The Associated Press reported.

This came after South Korea's National Intelligence Service (NIS) also said North Korea planned to send between 10,000 and 12,000 troops to Russia, according to Yonhap, a major South Korean news agency.

The NIS reportedly confirmed the “beginning of the North’s direct involvement” in Russia’s war in Ukraine.

Pyongyang is believed to have transported special forces from October 8 to 13, with around 1,500 North Korean soldiers transported in the first phase.

The soldiers were said to have been given Russian uniforms and weapons as well as fake IDs to disguise them as locals.

Newsweek has emailed the Russian Defense Ministry and the North Korean Mission of the Democratic People's Republic of Korea to the United Nations Office seeking comment.

NATO Secretary General Mark Rutte said allies had “no evidence that North Korean soldiers were involved in the fight.”

“But we know that North Korea is supporting Russia in many ways, whether through arms supplies, technological supplies or innovations to help it in the war effort – and that is extremely worrying,” he added.

A few days ago, reports emerged that an estimated 18 North Korean soldiers had left the front line in Russia.

The troops were stationed in Russia's Kursk and Bryansk oblasts, about four miles from the border with Ukraine, when they deserted, Ukraine's public broadcaster Suspilne reported.

Pyongyang and Moscow have been developing their relationship for some time and earlier this year pledged to provide mutual aid in the event of an attack.

Russian President Vladimir Putin visited North Korea in June for the first time in 24 years when he and Kim signed a so-called “comprehensive strategic partnership pact” with a clause similar to Article 5 of the North Atlantic Treaty Organization (NATO) that states that an attack on a member Attack on everyone is.

Should either country “enter a state of war due to armed aggression,” the other country “will immediately provide military and other assistance using all means at its disposal,” according to the pact published by North Korean state media.

Last week, South Korea's Defense Minister Kim Yong-hyun said: “Since Russia and North Korea have signed a mutual treaty similar to a military alliance, the possibility of such an operation is very likely.”