Islamic State militants have made more than $500 million trading oil with significant volumes sold to the government of Syrian President Bashar al-Assad and some finding its way to Turkey, a senior U.S. Treasury official said on Thursday.
The United States, France, Britain and Russia have vowed to defeat Islamic State, which uses an extreme interpretation of Islam to justify attacks and brutality in large parts of Syria and Iraq that it controls.
A U.S.-led coalition is bombing the hardline Sunni group, as is Assad's only big-power supporter Russia, in an attempt to kill its leaders and cripple the oil wells which the group uses to finance its rule and attacks abroad.
In one of the most detailed public explanations of Islamic State's oil trade, U.S. Treasury Department official Adam Szubin said militants were selling as much as $40 million a month of oil at the installations which was then spirited on trucks across the battlelines of the Syrian civil war and sometimes further.
"ISIL is selling a great deal of oil to the Assad regime," Szubin, acting under secretary for Terrorism and Financial Intelligence with the Treasury, told an audience at Chatham House in London.
"The two are trying to slaughter each other and they are still engaged in millions and millions of dollars of trade," Szubin said of Assad's government and Islamic State, also known as ISIS or ISIL.