The U.S. State Department expressed concerns over North Korea and Russia's strengthening cooperation upon news of North Korean foreign minister Choe Son-hui's trip to Russia from Monday through Wednesday.

In a written response to a media inquiry on Sunday, the department said the deepening cooperation between the two sides is a trend that should be of great concern to anyone interested in maintaining peace and stability on the Korean Peninsula and upholding the global nonproliferation regime.

Washington has been monitoring Pyongyang and Moscow's close cooperation, including the former's provision of conventional weapons to the latter in its war against Ukraine.

The White House, which last October revealed that the North had delivered over one-thousand containers of military equipment and munitions to Russia, announced earlier this month that several dozen ballistic missiles from the North had been used against Ukraine since late December.

Seoul's unification ministry spokesperson Koo Byoung-sam said on Monday that the international community has issued stern warnings against such Pyongyang-Moscow cooperation, adding Choe's visit will be closely monitored.

Earlier on Monday, the North's state-run Korean Central News Agency(KCNA) said a delegation led by Choe departed for Moscow on Sunday at the invitation of Russian foreign minister Sergey Lavrov.

[Photo : YONHAP News]