Russia’s defence ministry has accused Turkish President Recep Tayyip Erdogan of trading petroleum directly with the Islamic State group.
Deputy Defence Minister Anatoly Antonov said Turkey was the biggest buyer of “stolen” oil from Syria and Iraq.
Mr Erdogan said Russia had no right to “slander” Turkey with such claims.
Russia and Turkey have been locked in an angry dispute since Turkey shot down a Russian jet last month.
Russian President Vladimir Putin has already accused Ankara of downing the plane on its Syrian border to protect oil supply lines.