Russia's defense ministry said on Wednesday it had proof that Turkish President Recep Tayyip Erdogan and his family were benefiting from the illegal smuggling of oil from Islamic State-held territory in Syria and Iraq.
Moscow and Ankara have been locked in a war of words since last week when a Turkish air force jet shot down a Russian warplane near the Syrian-Turkish border, the most serious incident between Russia and a NATO state in half a century.
Erdogan responded by saying no one had the right to "slander" Turkey by accusing it of buying oil from Islamic State, and that he would stand down if such allegations were proven to be true. But speaking during a visit to Qatar, he also said he did not want relations with Moscow to worsen further.
At a briefing in Moscow, defense ministry officials displayed satellite images which they said showed columns of tanker trucks loading with oil at installations controlled by Islamic State in Syria and Iraq, and then crossing the border into neighboring Turkey.
The officials did not specify what direct evidence they had of the involvement of Erdogan and his family, an allegation that the Turkish president has vehemently denied.
"Turkey is the main consumer of the oil stolen from its rightful owners, Syria and Iraq. According to information we've received, the senior political leadership of the country - President Erdogan and his family - are involved in this criminal business," said Deputy Defense Minister Anatoly Antonov.
"Maybe I'm being too blunt, but one can only entrust control over this thieving business to one's closest associates."
"In the West, no one has asked questions about the fact that the Turkish president's son heads one of the biggest energy companies, or that his son-in-law has been appointed energy minister. What a marvelous family business!"
"The cynicism of the Turkish leadership knows no limits. Look what they're doing. They went into someone else's country, they are robbing it without compunction," Antonov said.
Erdogan last week denied that Turkey procures oil from anything other than legitimate sources.
He has said Ankara is taking active steps to prevent fuel smuggling, and he challenged anyone who accused his government of collaborating with Islamic State to prove their allegation