A monitoring group on Thursday said that a massive explosion hit near the Damascus International Airport in the early hours. The cause of explosion is not known.
"The blast was huge and could be heard in Damascus," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
Earlier on Tuesday, an air-strike in a rebel-held area outside Syria's capital Damascus killed nearly 16 civilians while wounding others.
The Eastern Ghouta region outside Damascus has been under a devastating government siege since 2012, and is also the regular target of regime air strikes and artillery fire.