A large explosion has hit an area near Damascus international airport, the Syrian Observatory for Human Rights says, the BBC reports.

“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.