A U.S. think tank says recent satellite photos show a sharp increase in rail traffic along the North Korea-Russia border, indicating the North is supplying munitions to Russia.

Beyond Parallel, a website run by the Washington-based Center for Strategic and International Studies think tank, made the assessment on Friday.

It says satellite images as of Thursday captured a dramatic and unprecedented level of freight railcar traffic at the Tumangang Rail Facility on the border.

Speculation about a possible North Korean plan to refill Russias drained arms inventory flared last month, when North Korean leader Kim Jong Un traveled to Russia to meet President Vladimir Putin.