SEOUL--South Korea’s top spy agency believes North Korea sent more than a million artillery shells to Russia since August to help fuel Russian President Vladimir Putin’s war on Ukraine, according to a lawmaker who attended a closed-door briefing Wednesday with intelligence officials.

North Korea and Russia have been actively boosting the visibility of their partnership in the face of separate, deepening confrontations with the United States. Their diplomacy — highlighted by a summit between North Korean leader Kim Jong Un and Putin in September — has triggered concerns about an arms arrangement in which North Korea supplies Russia with badly needed munitions in exchange for advanced Russian technologies that would strengthen Kim’s nuclear-armed military.

Both Pyongyang and Moscow have denied U.S. and South Korean claims that the North has been transferring arms supplies to Russia.

According to lawmaker Yoo Sang-bum, the South Korean National Intelligence Service believes the North shipped more than a million artillery shells to Russia through ships and other transport means since early August to help boost Russia’s warfighting capabilities in Ukraine. Those shells would roughly amount to two months’ worth of supplies for the Russians, Yoo said.

The agency believes North Korea has been operating its munitions factories at full capacity to meet Russian munition demands and has also been mobilizing residents to increase production, Yoo said. There are also signs that North Korea dispatched weapons experts to Russia in October to counsel Russian officials on how to use the exported North Korean weapons.

NIS officials didn’t immediately respond to a request to confirm Yoo’s account of the meeting. The agency has a mixed record on tracking developments in North Korea, which is made difficult by Pyongyang’s stringent control of information.

There are concerns in South Korea that North Korea could receive sensitive Russian technologies that would enhance the threat of Kim’s nuclear weapons and missiles program. But the NIS believes it’s more likely that the Russian assistance would be limited to conventional capabilities, possibly including efforts to improve North Korea’s aging fighter aircraft fleets, Yoo said.

It’s also likely that North Korea is receiving Russian technological assistance as it pushes ahead with plans to launch its first military reconnaissance satellite, Yoo quoted the NIS as saying. Following consecutive launch failures in recent months, the North failed to follow through on its vow to attempt a third launch in October. The NIS believes that the North is in the final phase of preparations for the third launch, which is more likely to be successful, Yoo said.

Kim has repeatedly described space-based reconnaissance capabilities as crucial for monitoring U.S. and South Korean military activities and enhancing the threat posed by his nuclear-capable missiles. Experts say the decision to meet Putin at Vostochny Cosmodrome, a major satellite launch facility in the Russian Far East, hinted at Kim’s desire to seek Russian technology assistance over spy satellites.

United Nations Security Council resolutions ban North Korean satellite launches because it views them as cover for testing long-range ballistic missile technologies.

The United States, South Korea and Japan issued a joint statement on Oct. 26 that strongly condemned what they described as North Korea’s supply of munitions and military equipment to Russia, saying that such weapons shipments sharply increase the human toll of Russia’s aggression in Ukraine.

The statement issued by the countries’ top diplomats came days after Foreign Minister Sergey Lavrov denied U.S. claims that his country received munitions from North Korea as he returned from a two-day trip to Pyongyang.

The White House had earlier said that North Korea had delivered more than 1,000 containers of military equipment and munitions to Russia. The White House released images that it said showed the containers were loaded onto a Russian-flagged ship before being moved via train to southwestern Russia.