The amount of oil smuggled into Turkey from areas of Syria controlled by the Islamic State is economically insignificant, the United States said Friday, after Moscow accused Ankara of profiting from the trade.

US officials said coalition air operations have seriously degraded the jihadists' oil infrastructure, but that in any case most of the crude pumped from its wells was absorbed inside Syria's war zone economy.

Russia and Turkey have in recent days traded allegations that they are involved in the illegal trade, further ratcheting up tensions after Turkish jets downed a Russian bomber on the Syrian border.

"The amount of oil being smuggled is extremely low and has decreased over time and is of no significance from a volume perspective -- both volume of oil and volume of revenue," said Amos Hochstein, US special envoy and coordinator for international energy affairs.

The State Department has dismissed Moscow's charge against its NATO ally, which directly implicated President Recep Tayyip Erdogan and his family in the trade, insisting there is no evidence to support it.

Officials on Friday confirmed that some small amount of oil may cross the Syria-Turkish border in tanker trucks, but not in quantities that would interest government officials.

"I don't believe that there is significant smuggling, between ISIL-controlled areas and Turkey of oil in any significance in volume," Hochstein said.

Instead, US officials told reporters, the oil pumped in eastern Syria is refined in ad hoc desert pits equipped with crude stills and sold on the war zone black-market within Syria and neighboring Iraq.

President Assad's government prefers not to buy IS oil when it has a choice, but in times of shortage is one of the customers of the middle-men and smugglers who bring trucks across Syria's network of front lines.

Allied officials estimated the IS group's income from oil at $1.0 to $1.5 million per day, but hope that renewed US, British and French air strikes have cut that.