Ukraine on Wednesday called on any North Korean troops fighting for Russia to surrender, after South Korea said over a thousand more had been deployed by Pyongyang.
South Korean lawmaker Park Sun-won said, after a briefing by his country's National Intelligence Service, that 1,500 more troops from the rival North had gone to Russia, taking the total deployment to 3,000.
"The planned deployment of about 10,000 troops from North Korea to Russia is expected to have occurred by December," added Park, who sits on the national assembly intelligence committee.
Neither Russia nor North Korea's state media have commented since Seoul's spy agency said last week said Pyongyang had decided to send a "large-scale" troop deployment to Russia to fight Ukraine.
But international concerns are mounting. Germany said Wednesday it had summoned North Korea's envoy over Pyongyang's support to Russia in Ukraine and warned the reclusive state against sending troops.
"North Korea's support of the Russian war of aggression directly threatens Germany's security and the European peace order," the German foreign ministry said on social media platform X.
The United States and NATO have not confirmed the deployment, but Ukrainian media reported President Volodymyr Zelensky saying Tuesday that two North Korean brigades -- up to 6,000 personnel each -- were being trained in Russia.
Ukraine on Wednesday called on any North Korean troops deployed by Russia to lay down their arms and save their lives.
"We address fighters of the Korean People's Army who were sent to help Putin's regime. You must not die senselessly in a foreign land," said a statement issued by an initiative run by Kyiv's military intelligence.
"You must not repeat the fate of hundreds of thousands of Russian soldiers who will never return home!" it added.
South Korea has said the nuclear-armed North is supplying Russia with weapons for use in Ukraine. The fresh alarm comes after the North's leader Kim Jong Un and Russian President Vladimir Putin signed a military deal in June.
Another lawmaker, Lee Seong-Kweun, said rumours were spreading within the tightly-controlled North that the elite "Storm Corps" had been sent to Russia.
"In response, North Korean authorities are said to be strictly controlling information, and there are indications that they are relocating and isolating the families of the deployed soldiers in undisclosed locations to better manage and control them."
South Korea will send a delegation to NATO headquarters in Brussels next week to brief the alliance on the situation, officials said.
Ukraine's appeal for North Korea troops to surrender came shortly after Zelensky made a new plea for allies to respond to the North's intervention.
"It is important that our partners do not hide from this challenge. All partners," he said in an address published late Tuesday.
"And if Russia is still able to make this war bigger and longer, then everyone in the world who is not helping to force Russia to peace is actually helping Putin to fight," he added.
The independent Russian Telegram channel Astra released clips Tuesday purportedly showing Russian and North Korean soldiers, with audio capturing phrases such as "I'm tired" and "we're late" spoken in a North Korean accent.
Lawmaker Lee said that Seoul's spy agency confirmed that the Russian military "is actively recruiting a large number of Korean language interpreters".
The North Korean troops are being trained on the use of drones and other technical skills, the lawmaker added.
"Russian instructors participating in military training have assessed that while the North Korean soldiers display excellent physical stamina and morale, they lack sufficient understanding of modern warfare tactics, especially drone-based attacks," Lee said.
As a result, Russian instructors expect "there could be a significant number of casualties if North Korean forces are deployed to the frontlines," Lee added.
Experts have said that in return for the troops, North Korea is likely aiming to acquire military technology, ranging from surveillance satellites to submarines, plus possible security guarantees from Moscow.
North Korea and Russia are under UN sanctions -- Kim for his nuclear weapons programme, and Moscow for the Ukraine war.
