The explosions were reported to have occurred in an undisclosed military area in Dummar, west of Damascus.
https://www.jpost.com/Breaking-News/Syrian-state-TV-Explosions-heard-in-Damascus-592611
https://www.ynetnews.com/articles/0,7340,L-5525541,00.html
http://www.israelnationalnews.com/News/AllFlashes.aspx
h/t NB