Russian intelligence has spotted nearly 12,000 oil-smuggling trucks near the Turkey-Iraq border, a top official in Moscow said. Russian forces have found the oil route during its reconnaissance missions and said the vehicles' final destination was Turkey.

"As of the moment of surveillance in the Zaho area, there were 11,775 fuel tanker trucks on both sides of the Turkish-Iraqi border. As many as 4,530 of them were on the territory of Turkey and 7,245 in Iraq," Russia's General Staff Main Operations Department's chief Sergey Rudskoy told reporters.

The lieutenant general added: "It must be noted that oil from both Iraq and Syria come through this [Zaho] checkpoint."

Satellite images of the heavy-duty trucks show the key route runs from Deir-ez-Zor province, which is controlled by Islamic State (Isis), through the border regions in Syria and eventually leads to Mosul, Iraq. The path, known as "eastern-route" in the region, was actively used by the IS (Daesh) militants to boost their revenue from oil, the Russian official added.

Moscow has been accusing Turkey of being involved in the oil trade with IS but Ankara refutes the allegations. Ever since Turkish jets brought down a Russian bomber aircraft, the two countries have been trading sharp accusations.

Russian forces said they have destroyed at least 2,000 oil tankers used by the extremists forcing them to change their routes frequently. Extraction and processing units operated by the Islamists have also been targeted by the Russian air strikes, Rudskoy added.

He said: "The northern and western routes which we previously revealed continue to be used. In order to avoid losses to Russian aviation, the terrorists move [the oil convoys] mainly at night. Moreover, their tanker trucks are disguised as ordinary lorries, and move in small columns of several dozen vehicles at a time."

Relations between Turkey and Russia have deteriorated since the downed jet incident. Turkish President Recep Tayyip Erdogan had earlier said he would step down if Russia was able to prove the allegations that Ankara was involved in any kind of oil trade with IS.