Turkish President Tayyip Erdogan said on Wednesday 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.
Erdogan, who was speaking at a university in Qatar's capital Doha, said he did not want relations with Moscow to worsen further.
"Nobody has the right to slander Turkey by saying Turkey is buying Daesh oil," he said, using an Arabic acronym for Islamic State.
Russia's defense ministry said it had proof that Erdogan and his family were benefiting from the illegal smuggling of oil from Islamic State-held territory in Syria and Iraq.