Britain's defense ministry has said it is "almost certain" that North Korean munitions have arrived in western Russia for the country's use in its war against Ukraine amid persistent speculation over their arms transfers.

The information followed Washington's revelation that Pyongyang had sent more than 1,000 containers of military equipment and munitions to Moscow as North Korean leader Kim Jong-un and Russian President Vladimir Putin held a rare summit last month.

"Despite Russia's official rejection of recent reports, it is almost certain that North Korean munitions have now reached ammunition depots in western Russia," the British ministry said in a post updated on X, formerly Twitter, on Thursday (local time).

"These depots support Russian military operations in Ukraine," it added.

The ministry said should Pyongyang continue to send military-related shipments at the current pace, it will be "on course" to become one of Moscow's "significant" overseas arms providers, alongside Iran and Belarus.

The international community has condemned the suspected arms agreement, which would violate multiple United Nations Security Council sanctions resolutions banning any weapons trade with the North, which Russia itself has voted for.

In a recent joint statement lambasting the two countries, Seoul, Washington and Tokyo confirmed part of such weapons deliveries and said the North is seeking military assistance to advance its own military capabilities.

Britain's defense ministry said while it is "unclear" what Moscow has agreed to provide to Pyongyang at the current stage, the package would likely include financial compensation, military technology provision and cooperation in other areas, such as space technology.

"It is unlikely the full package has been finalized," the ministry said, adding the package was likely among the top agenda items discussed in recent high-level exchanges between the two countries.

Citing commercial satellite imagery provided by Planet Labs, the U.S. media outlet Voice of America reported Friday that signs of cargo deliveries were detected at the North and Russia's border area and the North Korean port of Najin, reinforcing suspicions over their arms agreement. (Yonhap)