Speaking to Russian state television on Saturday, Foreign Minister Sergey V. Lavrov presented the framework agreement signed that day not as a response to a mass killing by the Assad government, but as a way to prevent Syria’s stockpiles of poison gas from falling into the hands of jihadist rebels.

Mr. Lavrov claimed that Russian investigators had established that “militants” were behind a number of previous chemical attacks in Syria, according to a translation of his remarks published on Monday by the Moscow news agency Interfax.

Making only vague reference to “lots of evidence delivered by independent experts onsite,” including “a nun from a local convent” and unnamed “eyewitnesses and Western reporters,” he went on to say that the Aug. 21 rocket attack with sarin gas on rebel-held areas outside Damascus had been staged. This conclusion was borne out, he said, by “European and U.S. experts, including 12 retired officers of the Pentagon and the C.I.A., who sent an open letter to President Barack Obama to explain how the case had been falsified.”