Russian tankers smuggled jet fuel to Syria through EU waters, bolstering military supplies to a war-torn country where Moscow is carrying out air strikes in support of the government, according to sources with knowledge of the matter.
At least two Russian-flagged ships made deliveries - which contravene EU sanctions - via Cyprus, an intelligence source with a European Union government told Reuters.
There was a sharp increase in shipments in October, said the source who spoke on condition of anonymity due to the sensitivity of the matter.
A separate shipping source familiar with the movements of the Russian-flagged vessels said the ships visited Cypriot and Greek ports before delivering fuel to Syria.
The Russian defence and transport ministries did not respond to requests for comment.
A spokeswoman for EU foreign affairs and security policy said the implementation of EU restrictions lay with member states.
Syria's civil war, which began in 2011, has become a theatre for competing global powers, with Russia and Iran supporting President Bashar al-Assad, and the United States, Gulf Arab and European powers backing rebels who want to depose him.
EU Council Regulation 1323/2014, introduced two years ago, bans any supply of jet fuel to Syria from the EU territories, whether or not the fuel originated in the European Union.
Over one two-week period in October, Russian tankers delivered 20,000 metric tonnes of jet fuel to Syria - worth around US$9 million at today's world prices - via the European Union, according to the EU government intelligence source.
"The jet fuel shipments from these vessels have played a vital role in maintaining Russian air strikes in the region," said the source. "This points to a sustained Russian build-up of resources needed to support their military operation and ambitions in Syria."
Some of the shipped fuel also went to the Syrian military, helping to "keep Assad's air assets operational", the source added.
The shipping source and a third person, an intelligence consultant specialising in the Mediterranean area, also said the fuel was likely intended for Russian and Syrian military use.