Russian tankers have supplied fuel to North Korea on at least three occasions in recent months by transferring cargoes at sea, Reuters reported Saturday.

Reuters, quoting two “senior Western European security sources,” said the transfers are providing an economic lifeline to North Korea. The sale of oil or oil products from Russia are in violation of U.N. sanctions, the sources told Reuters.

The transfers took place in October and November, Reuters reported.

“Russian vessels have made ship-to-ship transfers of petrochemicals to North Korean vessels on several occasions this year in breach of sanctions,” the first security source, who spoke on condition of anonymity, told Reuters.

A second source independently confirmed the existence of the Russian ship-to-ship fuel trade with North Korea. This source said there was no evidence of Russian state involvement in the latest transfers.

“There is no evidence that this is backed by the Russian state but these Russian vessels are giving a lifeline to the North Koreans,” the second European security source said.