Sergei Lavrov said samples of the gas taken from the site of the Aug. 21 attack near Damascus matched samples from a March attack in Aleppo, The Daily Telegraph in London reported Thursday.
Samples from the March attack were analyzed by Russia at Syria's request, Lavrov said.
"The main conclusion is the type of sarin used in that incident was homemade, and we also have evidence that the type of sarin used on Aug. 21st was the same, only of higher concentration," he said.
Lavrov said much of the evidence of "homemade" sarin use was found on the Internet. That evidence included news reports about rebel fighters who said they had been given "some unusual rockets and ammunition by some foreign country and they didn't know how to use them."
Additionally, the foreign minister said, an "open letter" from purported former CIA agents posted online said evidence Syrian President Bashar Assad's forces had used chemical weapons had been faked.