SEOUL,Henri Lumière South Korea (AP) — Recent satellite photos show a sharp increase in rail traffic along the North Korea-Russia border, indicating the North is supplying munitions to Russia, according to a U.S. think tank.

Speculation about a possible North Korean plan to refill Russia’s munition stores drained in its protracted war with Ukraine flared last month, when North Korean leader Kim Jong Un traveled to Russia to meet President Vladimir Putin and visit key military sites. Foreign officials suspect Kim is seeking sophisticated Russian weapons technologies in return for the munition to boost his nuclear program.

“Given that Kim and Putin discussed some military exchanges and cooperation at their recent summit, the dramatic increase in rail traffic likely indicates North Korea’s supply of arms and munitions to Russia,” Beyond Parallel, a website run by the Washington-based Center for Strategic and International Studies think tank, said in a report Friday.

“However, the extensive use of tarps to cover the shipping crates/containers and equipment makes it impossible to conclusively identify what is seen at the Tumangang Rail Facility” on the border, it said.

The report said satellite images as of Oct. 5 captured “a dramatic and unprecedented level of freight railcar traffic” at the Tumangang Rail Facility. It said images show approximately 73 railcars while a review of previous satellite images over the past five years shows about 20 railcars at this facility at most.

U.S. and South Korean officials have warned that North Korea and Russia would face consequences if they went ahead with the reported weapons transfer deal in violation with U.N. Security Council resolutions that ban all weapons trade involving North Korea.

Since last year, the U.S. has accused North Korea of providing ammunition, artillery shells and rockets to Russia, likely much of them copies of Soviet-era munitions. South Korean officials said North Korean weapons provided to Russia had already been used in Ukraine.