The flag of North Korea (Photo: EPA/AHMAD YUSNI)

Russia has used North Korean missiles against Ukraine at least 10 times, Jung Pak, a senior US official dealing with the issues of the Democratic People's Republic of Korea at the Department of State, told Voice of America.

"We are very concerned about this. There have been at least 10 incidents of North Korean missiles being used on the battlefield. So we are very concerned about what this means for future proliferation and how it makes things worse," she said.

The other day, the Minister of Defense of South Korea, Shin Won-sik, said that North Korea has sent approximately 7,000 containers with ammunition and other military equipment to Russia since last year.

According to the American official, "there were at least 10,000 containers that went from North Korea to Russia."

"There are almost certainly things that (North Korea) wants in return. And we're concerned about what might be going to the other side. We also worry about what the DPRK could be learning from Russia's use of these weapons and ballistic missiles on the battlefield, and how that might embolden and/or help the DPRK even further advance their weapons program," Jung Pak added.

On February 22, the Security Service of Ukraine reported that it had found confirmation of the use of KN-23/24 missiles from North Korea by the Russian military against Ukraine.

On February 27, South Korea's defense minister said that some North Korean defense factories are working at full capacity to produce weapons and ammunition for Russia.

On the same day, the United States and South Korea agreed to respond decisively to Pyongyang's transfer of weapons to Moscow.