North Korea has begun sending troops to Ukraine to fight Russia, South Korea’s spy agency said, as Seoul warned of a “serious security threat.”

The claim comes a day after Ukrainian President Volodymyr Zelensky said, based on intelligence, he believed 10,000 North Korean soldiers could join the war.

South Korean President Yoon Suk Yeol called a security meeting on Friday and said the international community must respond with “all available means.”

According to the secret service, 1,500 soldiers have already arrived in Russia – anonymous sources tell South Korean media that the final number could be closer to 12,000.

This comes at a time when evidence is mounting that North Korea is supplying Russia with munitions, as recently demonstrated by the recovery of a missile in Ukraine’s Poltava region.

Moscow and Pyongyang have also deepened their cooperation in recent months. Last week, North Korean leader Kim Jong Un greeted Russian President Vladimir Putin on his birthday. calls him his “closest comrade”.

Friday’s security meeting was attended by key officials from South Korea’s National Security Office, Defense Ministry and National Intelligence Agency, Yoon’s office said.

“(The participants) decided not to ignore the situation and, together with the international community, to respond to it using all available means,” it said.

The National Intelligence Service (NIS) claim comes days after Ukrainian military intelligence sources said the Russian army was creating a unit made up of North Koreans.

The BBC has contacted the NIS for comment.

On Thursday, Ukrainian intelligence chief Kyrylo Budanov claimed that nearly 11,000 North Korean infantry troops were being trained in eastern Russia to fight in Ukraine.

“They will be ready (to fight in Ukraine) on November 1,” said Lt. Gen. Budanov, who heads Ukraine’s Defense Intelligence Directorate. said the Warzone website.

He added that the North Koreans would use Russian equipment and ammunition and the first group of 2,600 troops would be sent to Russia’s western Kursk region, where Ukraine has a number of settlements after the start of his invasion in August.

Earlier this week, Putin introduced a bill to ratify a military pact he made with Kim that promises Russia and North Korea will support each other in the event of “aggression” against either country.

South Korea’s spy agency NIS said North Korean troops were training at Russian bases in Vladivostok, Ussuriysk, Khabarovsk and Vlagoveshensk.

This appears to confirm information from a military source in the Russian Far East, who told BBC Russian this week that “a number of North Koreans have arrived” and are stationed at one of the military bases near Ussuriysk.

Seoul’s intelligence agency also released aerial photos of Ussuriysk and Khabarovsk, where hundreds of North Korean troops have reportedly gathered, as well as another photo of the North Korean port of Chongjin, where a Russian ship carrying North Korean soldiers was reportedly seen.

The NIS said it found that North Korea had sent 13,000 shipping containers containing grenades, rockets and anti-tank missiles to Russia since August.

Up to eight million 122mm and 152mm shells were delivered to Russia, it said.

However, some military experts believe that Russian military units will have difficulty integrating North Korean troops on their front lines.

Apart from the language barrier, the North Korean army has no current combat experience, it said.

“They could guard some sections of the Russian-Ukrainian border, freeing up Russian units to fight elsewhere,” said Valeriy Ryabykh, editor of the Ukrainian publication Defense Express.

“I would rule out the possibility of these units appearing at the front immediately.”

Additional reporting from Jake Kwon and Hosu Lee in Seoul