Rail traffic along the border between North Korea and Russia rose to its highest level in years this week, suggesting Pyongyang is supplying Moscow with weapons after their leaders discussed closer military cooperation, Reuters, a US think tank, said.

Satellite images showed an “unprecedented” number of about 73 freight cars at the Tumangang railway station in the North Korean border city of Rason, according to a report by the Beyond Parallel Project of the Center for Strategic and International Studies in Washington.

The railway traffic was much higher than that observed in the last five years, including in the pre-pandemic period, the organization said.

North Korean leader Kim Jong Un and Russian President Vladimir Putin held a weeklong summit in the Russian Far East last month, where they discussed military issues, the war in Ukraine and deepening military-economic cooperation.

“Given that Putin and Kim discussed some military exchanges and cooperation at their recent summit, the sharp increase in rail traffic likely indicates North Korea’s supply of arms and ammunition to Russia,” the think tank said, saying it did not can say this with confidence, because the tarpaulin with which the wagons are covered.

The US and South Korea have warned that this military cooperation between North Korea and Russia is a violation of UN sanctions against Pyongyang.

They expressed concern that Moscow could look to North Korea for munitions to bolster its dwindling stockpiles for an invasion of Ukraine, while Pyongyang could seek technological help for its satellite and missile programs.