"As four months have passed for the dispatch of troops for the Russia-Ukraine war, and multiple casualties and captives have occurred, (North Korea) is suspected to be accelerating follow-up measures and preparation for an additional dispatch of troops," the Joint Chiefs of Staff (JCS) said in a statement.
The JCS analysis did not specify what other follow-up measures Pyongyang might take.
North Korea is also preparing to launch a spy satellite and an intercontinental ballistic missile (ICBM), though there were no signs of immediate action, the JCS said.
This month, Ukrainian President Volodymyr Zelenskiy said two North Korean soldiers had been captured in Russia's Kursk region, marking the first time Ukraine had taken North Korean soldiers alive since their entry into the war last autumn.
Pyongyang has deployed about 11,000 soldiers to support Moscow's forces in Russia's western Kursk region, according to Ukrainian and Western assessments, which Ukraine seized in a surprise attack last year.
More than 3,000 have been killed or wounded, according to Kyiv.
Although Moscow and Pyongyang initially dismissed reports about the North's troop deployment, Russian President Vladimir Putin in October did not deny that North Korean soldiers were in Russia and a North Korean official said any such deployment would be lawful.
The escalating cooperation comes after Putin's visit to Pyongyang in June 2024, where the leaders signed a "Comprehensive Strategic Partnership Treaty", which includes a mutual defence pact.
