The United States will not hesitate to impose sanctions on North Korea and Russia when necessary, a state department spokesperson said Monday, following the Russian defense minister's trip to Pyongyang that many believe may lead to increased military cooperation between the two countries.

The spokesperson, Matthew Miller, also highlighted that the close relationship between Pyongyang and Moscow has "not exactly been productive" to international security.

"It certainly did not appear that Defense Minister (Sergei) Shoigu was in North Korea for vacation," the department spokesperson said when asked about the Russian defense minister's visit to Pyongyang last week for events marking the 70th anniversary of the Korean War armistice, which is celebrated in North Korea as Victory Day.

"I am not going to speak anymore in any more detail, but will say that we have imposed a number of sanctions on North Korea in the past for various activities, but also imposed sanctions on a number of entities and individuals around the world for assisting Russia in its war effort. We won't hesitate to do so in the future," Miller told a press briefing.

His remark follows an earlier report that Ukraine has been firing North Korean rockets seized from a ship that was potentially headed to Russia, indicating an apparently ongoing weapons trade between North Korea and Russia.

Seoul stressed that any weapons trade with North Korea directly violates United Nations Security Council resolutions.

"We have never hesitated to impose sanctions on North Korea and North Korean entities when we found violations or we found actions that merit sanctions, and we won't hesitate to do so in future," Miller reiterated.

"Obviously, there has been a close relationship between those two countries for a while," he added when asked about Russia-North Korea cooperation. "When that's not exactly been productive to increasing the security of the world, I wouldn't expect that to change as a result of this." (Yonhap)