The United States and its main allies said on Friday they are "gravely concerned" by deepening cooperation between North Korea and Russia and called for an end to North Korean arms transfers for use against Ukraine.

The U.S. Secretary of State and foreign ministers from Australia, Canada, France, Germany, Italy, Japan, New Zealand, South Korea and Britain, as well as the EU High Representative, issued a joint statement highlighting their recent coordination of sanctions measures in response to such activity.

"Our governments stand in resolute opposition to these continued arms transfers, which Russia has used to strike Ukraine's critical infrastructure, prolonging the suffering of the Ukrainian people," they said.

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"We are gravely concerned by the deepening DPRK-Russia cooperation" in "flagrant violation" of multiple U.N. Security Council resolutions, the statement said, referring to North Korea by the initials of its official name.

Moscow and Pyongyang have denied accusations of arms transfers, but vowed last year to deepen military relations.

Friday's joint statement condemned Russia's March veto of a U.N. resolution that would have extended the mandate of an expert panel tasked with monitoring the implementation of U.N. sanctions against North Korea.

"We call on the DPRK and Russia to cease unlawful arms transfers," the statement said.

Days before its mandate expired, the U.N. panel submitted a report confirming that, in a violation of U.N. sanctions, a North Korean-made ballistic missile known as Hwasong-11 had struck the Ukrainian city of Kharkiv.

Since Russia's veto, the U.S. and its allies have sought alternative ways to coordinate and monitor sanctions on North Korea. The alleged North Korean arms transfers to Russia have also prompted responses from South Korea and Japan, Britain and elsewhere.

A spokesperson for the U.S. State Department called it "the largest multilateral coordinated DPRK sanctions action to date."

"We urge both countries to immediately halt their malign activities," the spokesperson said.

The joint statement called on North Korea to take concrete steps towards abandoning its nuclear weapons and ballistic missile programs and to return to diplomacy.