Russia’s defence ministry has accused the family of Turkish President Recep Tayyip Erdogan of being directly involved in the trade of petroleum with the Islamic State group.
At a briefing to journalists in Moscow, deputy defence minister Anatoly Antonov said Turkey was the biggest buyer of “stolen” oil from Syria and Iraq.
Mr Erdogan has promised to resign if the smuggling claims are substantiated.
Turkey shot down a Russian jet inside Syria on 24 November, raising tensions.
“According to available information, the highest level of the political leadership of the country, President Erdogan and his family, are involved in this criminal business,” Mr Antonov told the briefing.
The defence ministry cited satellite images that it said showed oil tankers travelling from IS-held territory to Turkey.
The trucks, it said, travelled to three locations – including refineries – in Turkey and some was then moved on to a third country.
Russia said it was producing only “part of the evidence” for now.
Moscow had already claimed that Turkey benefited from IS oil sales.
On Monday, Mr Erdogan challenged his Russian counterpart to produce evidence to back up the claim – and he would resign if it was found to be true.
“As soon as such a claim is proved, the nobility of our nation requires [me] to do this,” he said. “I will not remain in this post. But I am asking Mr Putin, would you remain?”
Russia and Turkey have been involved in tit-for-tat exchanges since the downing of the jet. Last week, Moscow imposed visa requirements for Turkish visitors, and placed restrictions on trade with Ankara.