Apologies that was rather unclear, the most recent attack is unproven however the U.N. inspectors that investigated the 2013 attack said in their report:
The UN report on the investigation into the Ghouta chemical attacks was published on 16 September 2013. The report stated: "the environmental, chemical and medical samples we have collected provide clear and convincing evidence that surface-to-surface rockets containing the nerve agent sarin were used in Ein Tarma, Moadamiyah and Zamalka in the Ghouta area of Damascus."
[18](p
[30] UN Secretary-General Ban Ki-moon called the findings "beyond doubt and beyond the pale," and clear evidence of a war crime. "The results are overwhelming and indisputable," he said. Ban stated a majority of the blood samples, environmental samples and rockets or rocket fragments recovered tested positive for sarin.
[111] The report, which was "careful not to blame either side," said that during the mission's work in areas under rebel control, "individuals arrived carrying other suspected munitions indicating that such potential evidence is being moved and possibly manipulated."
[112] The UN investigators were accompanied by a rebel leader.