It would be a "dangerous and highly concerning development" if North Korea was sending troops to help Russia in Ukraine, the United States said on Monday as South Korea and Britain warned of the high price Moscow would likely have to pay Pyongyang.

"We are consulting with our allies and partners on the implications of such a dramatic move," deputy U.S. Ambassador to the UN Robert Wood told the 15-member United Nations Security Council. Russia invaded neighbouring Ukraine in February 2022.

Ukrainian President Volodymyr Zelenskyy has accused Pyongyang of preparing to send 10,000 soldiers to Russia. Ukraine's UN Ambassador Sergiy Kyslytsya told the Security Council on Monday: "These troops are expected to be ready for war against Ukraine by November 1."

South Korea's spy agency said last week that North Korea had shipped 1,500 special forces troops to Russia's Far East for training and acclimatizing at military bases and that they were likely to be deployed for combat in Ukraine.

"If true, this marks a dangerous and highly concerning development and an obvious deepening of the DPRK, Russia military relationship," Wood said of the reports, using North Korea's formal name, the Democratic People's Republic of Korea.

'Scare mongering'

The Kremlin earlier on Monday declined to directly answer a query on whether North Korean troops were going to fight in Ukraine, but spokesman Dmitry Peskov said Moscow's cooperation with Pyongyang was not directed against third countries.

Russia's UN Ambassador Vassily Nebenzia accused Western countries of becoming "distracted by circulating scare mongering with Iranian, Chinese and Korean bogeymen, each one of which is more absurd than the one before."

Britain's UN Ambassador Barbara Woodward said it was "highly likely" that North Korea was sending troops.

"It seems that the harder [Russian President Vladimir] Putin finds it to recruit Russians to be cannon fodder, the more willing he is to rely on DPRK in his illegal war," she said. "We can be certain that the DPRK leadership will ask a high price from Russia in return."

South Korea's UN Ambassador Joonkook Hwang also warned the council of the implications of such a move.

"North Korea will expect a generous payoff from Moscow in return for its troop contribution. It could be either military or financial assistance. It could be nuclear weapons-related technology," he said.

North Korea has been under UN sanctions since 2006 for its nuclear and ballistic missile programs, and those measures have been strengthened over the years — with Russia's support.