The volume of Daesh oil smuggled into Turkey is "extremely low" and has decreased over time, a senior U.S. State Department official said Friday.

The anonymous official, speaking to reporters, also rejected claims by the Russian Defense Ministry that senior Turkish officials were involved in oil smuggling from Syria.

"Our assessment is that there is not a lot of smuggling happening of any significant volume between ISIL [Daesh]-controlled territories and Turkey," the official said.

"The volume itself of the oil being smuggled is extremely low and has decreased over time."

According to the official, most of the oil smuggled from Daesh-controlled areas was going into Syrian regime strongholds and Iraq.

"The oil is being consumed [is] almost entirely inside areas of control of Syria and trading with the regime," he added, referring to Bashar al-Assad government.

The senior official noted that to smuggle 20,000 barrels of oil into Turkey -- which he described at "the low end for significant" volume -- at least 1,000 would be employed to carry that amount of oil.

"The economics don`t make sense for that to happen," the official said. "The evidence doesn`t suggest that we would see thousands of trucks going through this territory and it would have to cross several different areas of control, and at every point have to pay fees."

The official flatly rejected claims that Turkey, a NATO ally and partner in the anti-Daesh coalition, was involved in the black-market oil trade or any transaction with Daesh.

U.S. and French aircraft have been striking oil facilities and tanker trucks carrying smuggled oil from Daesh-controlled areas.

The U.S. Treasury earlier this week imposed sanctions on a Syrian citizen and his firm for facilitating oil trade between Daesh and the Assad regime as well as some Russians for supporting the regime financially.

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