"We have warned Russia of the illicit North Korean coal trading through its ports. Russia says it will follow all UNSCRs, but it fails to enforce them and rewards illegal behavior by the DPRK. There is no more time for excuses," Nauert wrote in the statement via Twitter.
Last week, Reuters news agency reported, citing Western European intelligence sources, that North Korea imported coal to Russia after which the shipments were delivered to Japan and South Korea in violation of existing UN sanctions against Pyongyang.
North Korea has faced several rounds of sanctions over its nuclear and ballistic missile tests, conducted in violation of the UN Security Council (UNSC) resolutions. In response to these activities, in August the UNSC imposed sanctions on Pyongyang targeting exports of coal, iron ore, lead and seafood from the Asian nation to UN member states. In December, new sanctions against North Korea were imposed over the country's continuing missile tests.