Meanwhile, the United States said for the first time on Wednesday that it had seen evidence of North Korean troops in Russia.

U.S. Defense Secretary Lloyd Austin, speaking in Rome, said it would be "very, very serious" if the North Koreans were preparing to fight alongside Russia in Ukraine, as Kyiv has alleged, though he said it remained to be seen what they would be doing there.

"There is evidence that there are DPRK troops in Russia," Austin told reporters, using North Korea’s formal name, the Democratic People’s Republic of Korea.

In Seoul, South Korean lawmakers said that North Korea has sent 3,000 troops to Russia and thousands more were expected to follow.

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Pyongyang had promised to provide a total of about 10,000 troops, whose deployment was expected to be completed by December, the lawmakers told reporters after being briefed by South Korea’s national intelligence agency.

The figure of 3,000 is twice a previous estimate of numbers of troops already in Russia.

"Signs of troops being trained inside North Korea were detected in September and October," Park Sun-won, a member of a parliamentary intelligence committee, said after the briefing.

"It appears that the troops have now been dispersed to multiple training facilities in Russia and are adapting to the local environment."

The Ukraine conflict broke out when Russia invaded its neighbour in February 2022 and has since developed into a war of attrition largely fought along front lines in eastern Ukraine, with huge numbers of casualties on both sides.

Austin said the alleged North Korean deployment could be further evidence that the Russian military was having problems with manpower.

The Kremlin has previously dismissed Seoul s claims about the North’s troop deployment as "fake news" and a North Korean representative to the United Nations in New York called it "groundless rumours" at a meeting on Monday.

Both Moscow and Pyongyang have also denied weapons transfers, but they have pledged to boost military ties and signed a mutual defence treaty at a summit in June.

The latest numbers came after Seoul s National Intelligence Service said on Friday the North had sent some 1,500 special forces personnel to Russia by ship and they were likely to be deployed for combat in the war in Ukraine after training and acclimatisation.

Ukrainian President Volodymyr Zelenskiy has also accused Pyongyang of preparing to send 10,000 soldiers to Russia. On Tuesday he called on his allies to respond to evidence of North Korean involvement in Russia s war.

FAMILIES ISOLATED

Lee Seong-kweun, a lawmaker on the South Korean committee, said Pyongyang authorities had tried to keep news of the deployment from spreading.

"There are also signs of North Korean authorities relocating and isolating those families (of the troops) in a certain place in order to effectively control them and thoroughly crack down on the rumours," Lee said, citing the spy agency.

Lee also said the agency confirmed that Russia had recruited a "large number" of interpreters for the North Korean soldiers, while training them in the use of military equipment such as drones.

"Russian instructors are assessing that the North Korean military has excellent physical attributes and morale but lacks understanding of modern warfare such as drone attacks," he said.

"Therefore there could be many casualties if they are deployed to the front lines."

U.S. officials, speaking on condition of anonymity, say Russia has suffered more than 600,000 killed or wounded troops in the war in Ukraine.

Austin said the alleged North Korean deployment could point to a shortage of Russian recruits.

"This is an indication that he (Russian President Vladimir Putin) may be even in more trouble than most people realize," Austin said.

On Tuesday the South s presidential office urged an immediate withdrawal of the North’s troops from Russia, warning that it may consider supplying lethal weapons to Ukraine if military ties between them went too far.

In Berlin, Germany summoned North Korea’s charge d affaires on Wednesday over concerns about the troop deployment.

"Should reports be true on North Korean soldiers in Ukraine and should North Korea now be supporting the Russian war of aggression in Ukraine with troops, this would be serious and in violation of international law," the German foreign ministry said.

South Korea s National Intelligence Service said last week it had been working with the Ukrainian intelligence service and had used facial recognition technology to identify North Korean officers in eastern Ukraine’s Donetsk region supporting Russian forces firing North Korean missiles.