Washington DC - Ten countries and the EU called North Korea's growing involvement in Russia's war in Ukraine a "dangerous expansion" on Monday, in a joint statement released by the United States.

Pyongyang has sent thousands of troops to reinforce Russia's war effort, including to the Kursk border region, where Ukraine reported Monday that its fighters had killed or wounded at least 30 North Korean soldiers.

"Direct DPRK support for Russia's war of aggression against Ukraine marks a dangerous expansion of the conflict, with serious consequences for European and Indo-Pacific security," the statement said, referring to North Korea by its official acronym.

The foreign ministers of Australia, Canada, France, Germany, Italy, Japan, South Korea, New Zealand, the UK, the US, and the high representative of the European Union signed the release.

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They also said that they were "deeply concerned about any political, military, or economic support that Russia may be providing to the DPRK's illegal weapons programs, including weapons of mass destruction."

North Korea and Russia have strengthened their military ties since Moscow's invasion of Ukraine in February 2022.

Experts say the nuclear-armed North's leader, Kim Jong Un, is keen to acquire advanced technology from Moscow and battle experience for his troops.

The statement signatories said they "condemn in the strongest possible terms the increasing military cooperation," including the "deployment of DPRK troops to Russia for use on the battlefield against Ukraine."

They added that the export of ballistic missiles, artillery shells, and other military material by Pyongyang to Russia, as well as Moscow's training of North Korean soldiers involving arms, "represent flagrant violations of United Nations Security Council resolutions."

"We urge the DPRK to cease immediately all assistance for Russia's war of aggression against Ukraine, including by withdrawing its troops," the statement said.

The US and South Korea have accused the North of sending more than 10,000 soldiers.