Russian tankers have reportedly repeatedly supplied fuel to North Korea in a violation of sanctions on the isolated state.

Reuters said two Western European security officials had said Russian ships were transferring their cargo at sea to Korean vessels.

A source told the news agency there was no evidence that the transfers were state-sponsored but noted the transfers were nevertheless “giving a lifeline” to North Korea, which has faced global condemnation for its increasing belligerent behaviour.

Russian officials declined to comment and the owner of a ship allegedly implicated denied any involvement.

But the allegations that Russian ships have been thwarting sanctions intended to stifle the North Korean economy demonstrate the types of hurdles the international community faces in seeking to alter North Korea’s militaristic ambitions through diplomatic means.

As North Korea has hurled ballistic missiles over Japan, tested a hydrogen bomb and threatened Asian neighbours with annihilation, the United Nations has imposed a series of sanctions intended to weaken the nation’s economy and punish its leadership.