The sales of oil or oil products from Russia, the world’s second biggest oil exporter and a veto-wielding member of the United Nations Security Council, breach U.N. sanctions, the security sources said.

The transfers in October and November indicate that smuggling from Russia to North Korea has evolved to loading cargoes at sea since Reuters reported in September that North Korean ships were sailing directly from Russia to their homeland.

“The Russian vessels made transfers at sea to the North Koreans,” the first security source, who spoke on condition of anonymity, told Reuters. The source said the transfers of oil or oil products took place on several occasions and were a breach of sanctions.