A Japanese daily said on Friday that North Korean tankers appear to have shipped oil supplied by Russia to North Korea in April.

The Yomiuri Shimbun said that its analysis of satellite imagery indicated that four North Korean tankers shipped refined petroleum from Vostochny Port in the Russian Far East to Nampo in North Korea in early April. 

UN Security Council sanctions set an annual 500-thousand-barrel global cap on refined petroleum products to North Korea.

The Yomiuri said that it analyzed satellite images from U.S. company Planet Labs along with Katsuhisa Furukawa, a former member of the experts’ panel of the UN Security Council's Sanctions Committee on North Korea. 

Furukawa reportedly said that since this spring, North Korean oil tankers have been shipping refined petroleum products directly from Vostochny Port, indicating UN sanctions are not working.