A large explosion has hit an area near Damascus international airport, the Syrian Observatory for Human Rights says.
“The blast was huge and could be heard in Damascus,” said Rami Abdel Rahman, head of the UK-based monitoring group.
The airport lies about 25 km (15 miles) south-east of Syria’s capital.
The blast was reportedly followed by a large fire. There is no word on casualties. The cause is unclear.
Syria has been embroiled in a civil war since 2011.
The conflict has killed more than 320,000 people and, after more than six years, no political solution to the fighting is in sight.
While Damascus has remained relatively insulated from the violence, fighting between the military and rebels has erupted near the capital in recent months.
Last month, there were reports that Syrian government forces were bombarding eastern areas of Damascus after rebel fighters launched a surprise offensive.