North Korea sent an additional 3,000 troops to Russia this year and is still supplying missiles, artillery and ammunition to help Moscow fight Kyiv, Seoul's military said on Thursday.
Traditional allies Russia and North Korea have drawn closer since Moscow's 2022 invasion of Ukraine, with Seoul accusing leader Kim Jong Un of sending thousands of troops and containers of weapons to help Moscow.
Neither Moscow nor Pyongyang has officially confirmed the troop deployment but the two countries signed a sweeping military deal last year, including a mutual defense clause, when Russian President Vladimir Putin made a rare visit to North Korea.
"It is estimated that an additional 3,000 troops were sent between January and February as reinforcements," South Korea's Joint Chiefs of Staff said.
It said that, of the initial 11,000 North Korean soldiers sent to Russia, 4,000 are believed to have been killed or wounded.
"In addition to manpower, North Korea continues to supply missiles, artillery equipment, and ammunition," the report by the JCS said.
"So far, it is assessed that North Korea has provided a significant quantity of short-range ballistic missiles (SRBMs), as well as about 220 units of 170mm self-propelled guns and 240mm multiple rocket launchers," it said.
It warned that "these numbers could increase depending on the situation on the battlefield".
North Korea launched a flurry of ballistic missiles last year in violation of UN sanctions.
Experts have warned that the nuclear-armed North may be testing weapons for export to Russia for use against Ukraine.
Attack drones
North Korean state media reported on Thursday that Kim oversaw the test of new suicide and reconnaissance drones featuring artificial intelligence technology.
The new strategic reconnaissance drone is capable of "tracking and monitoring different strategic targets and enemy troops' activities on the ground and the sea", the Korean Central News Agency (KCNA) said.
The suicide drones also demonstrated the striking capability "to be used for various tactical attack missions", according to KCNA.
Kim evaluated the improved performance of "the strategic reconnaissance drone... and the suicide attack drones with the introduction of new artificial intelligence".
He also agreed to a plan "for expanding the production capacity", KCNA said.
Pyongyang unveiled its attack drones last August, with experts saying the new capability in this area could be attributable to the North's budding alliance with Russia.
Experts have also warned that North Korean troops sent to fight for Russia will be gaining modern warfare experience, including how drones are used on the battlefield.
North Korea is now focusing on "unmanned weapon systems like drones because this is broadly part of their five-year defense development plan", Yang Moo-jin, the president of the University of North Korean Studies, told AFP.
In 2024, North Korea claimed that the South had sent drones over Pyongyang -- something Seoul's Ministry of Defense has denied.
This, coupled with the drone attacks experienced by North Korean troops fighting with Russia, has "likely made Chairman Kim Jong Un feel the urgency to complete these drone weapon systems quickly".
This would require sufficient scientific technology and funding and "considering that Russia does have some level of technological capability, we can assume that part of the motivation for dispatching troops might be to gain access to that technology", Yang said.
The JCS report comes four months after Kim ordered the "mass production" of attack drones that are designed to carry explosives and be deliberately crashed into enemy targets, effectively acting as guided missiles.
Pyongyang sent drones across the border in 2022 that Seoul's military was unable to shoot down, saying they were too small.
