The Russian foreign ministry said in a statement carried by Russian news agencies that Russia has "fully and strictly observed the sanctions regime". According to the experts, the trade in oil and petroleum products was made through transfers from Russian to North Korean tankers in open waters.
The sale of oil or oil-products from Russian Federation, the world's second biggest oil exporter and a veto-wielding member of the United Nations Security Council, breaches UN sanctions, Reuters quoted the security sources as saying.
The resolution included sharply reduced limits on North Korea's refined oil imports, the return home of all North Koreans working overseas within 24 months, and a crackdown on ships smuggling banned items including coal and oil to and from the country.
One of the sources said there was nothing to suggest Russian state involvement in the latest transfers.
The two security sources cited naval intelligence and satellite imagery of the ships operating out of Russian Far Eastern ports, but could not reveal further details.
The Vityaz at least once appears to have gone out telling the Russian government their destination was a Russian fishing fleet in the Sea of Japan, but ended up meeting a Korean tanker instead, one which had its transponder off.
Reuters could not independently verify the transfer as ship tracking data showed that the Sam Ma 2 had turned off its transponder from the start of August.
Yaroslav Guk, deputy director of the tanker's owner, Vladivostok-based Alisa Ltd, said the vessel had no contacts with North Korean vessels. "It would be complete madness".
The claims come after Russian Federation offered to mediate between the United States and North Korea as the Kremlin said it wanted "to clear the way for de-escalation".
Russia observes fully the sanctions regime against the DPRK, announced by the UN Security Council, the Foreign Ministry's press service said on Saturday in a comment on reports in the media, claiming Russian tankers made a few trips to North Korea.
The reports came a day after China denied similar accusations. On Thursday the United States president said Beijing had been "caught red-handed" and that he was "very disappointed that China is allowing oil to go into North Korea". Three North Korean ships among the 10 were blacklisted, along with a Panama-registered vessel.