(Bloomberg) -- A Russian cargo plane under US sanctions touched down in Pyongyang this week for an unannounced trip that raised concerns about illegal arms transfers, a specialist news service reported. 

The Ilyushin 76TD plane linked to Russia’s military departed from Shanghai on Monday and made a sharp turn toward North Korea, NK News reported Wednesday based on data from commercial tracking service FlightRadar24.

The plane departed for Tianjin, southeast of Beijing and then left for Moscow on Tuesday, it said. NK News, a Seoul-based provider of news on North Korea, said there was no commercial satellite imagery showing the Russian cargo plane on the ground in Pyongyang. But the South Korean DongA Ilbo newspaper said it was there for several hours, giving workers enough time to unload and load cargo. 

There was no mention on the flight in North Korea’s official media. NK News said the tail number of the plane was the same as an Ilyushin 76TD cargo plane sanctioned by the US Treasury in January 2023 when it took action to “degrade the Russian Federation’s capacity to wage war against Ukraine.”

South Korea’s Ministry of National Defense did not comment on the flight. It did say in a statement that “South Korea and the US have been tracking and monitoring related signs.”

While it is uncertain what may have been on board the plane, flights of military-related planes between Russia and North Korea have been rare in recent years and thought by weapons experts to be linked to the transfer of arms by Kim Jong Un’s regime to help President Vladimir Putin in his assault on Ukraine.

Last year, there were two flights tracked by FlightRadar24 that caught attention, including a Russian military VIP plane that touched down in Pyongyang days after Defense Minister Sergei Shoigu traveled to the North Korean capital to attend a military parade hosted by Kim, who also gave him a tour of a weapons exhibit. Another Russian military VIP plane landed in Pyongyang in September, stoking concerns that it transported officials for arms deals.

North Korea and Russia did not comment on either flight and have denied accusations from the US, Japan, South Korea and others of the arms transfers.

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After the flights, satellite imagery showed sea traffic picking up between the once sleepy North Korean port of Najin near the border of Russia and Dunay, a former Soviet submarine base about 180 kilometers (110 miles) away. The White House provided imagery it said showed weapons being sent on the route and delivered thousands of miles away to a depot in the Russian town of Tikhoretsk for use in Ukraine.

North Korea has shipped containers that could hold as many as 3 million rounds of artillery shells to Russia, South Korean Defense Minister Shin Wonsik told reporters last month. This could allow Putin to maintain his assault on Ukraine as Kyiv’s stocks of ammunition dwindle.

Kyiv is estimated to need at least 200,000 rounds a month to keep up the fight against Russia’s invading forces, whose average daily shell use can be anywhere from three to five times what Ukrainian forces can fire. 

Russia in return for munitions and ballistic missiles is providing North Korea with food, raw materials and parts used in weapons manufacturing, Shin said. The food aid has helped Kim stabilize prices for necessities, he said, adding if the arms transfers grow, Russia is set to send more military technology to Kim, which increases Pyongyang’s ability to threaten the region.

The sea trade may have briefly slowed in the past few weeks. One of the vessels named by the US as involved in the trade and subject to US Treasury sanctions, the Russian cargo ship Angara, appears to be at a dry-dock facility in China for repairs, maritime tracking data indicates. 

Satellite imagery from Sunday showed another Russia cargo ship thought to have gone in for repairs, the Lady R, has returned to the port in North Korea, NK News reported. 

President Joe Biden announced Tuesday the US is offering a fresh package of $300 million for Ukraine, with the funds coming from contract savings on weapons bought to replenish those sent to Kyiv earlier. Biden cautioned that package was “not nearly enough.” 

--With assistance from Shinhye Kang, Soo-Hyang Choi and Danny Lee.

©2024 Bloomberg L.P.