The pro-Hezbollah al-Manar television channel said that an explosion at fuel tanks and warehouses near Syria's Damascus International Airport early on Thursday had likely been caused by an Israeli air strike.

It added that initial indications were that the blast had caused only material damage and not deaths.

Hezbollah, an ally of Assad regime, is involved in the fighting in Syria's civil war.

"The blast was huge and could be heard in Damascus," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.

The Damascus International Airport lies about 25 kilometres southeast of Syria's capital.

The Britain-based Observatory, which gathers information from sources across war-ravaged Syria, said it had confirmed the explosion had not taken place inside the airport itself.

More than 320,000 people have been killed since Syria's conflict erupted in 2011 with widespread anti-government protests.

While Damascus has remained relatively insulated from the violence, fierce fighting has raged on the outskirts of the capital in recent months between opposition groups and regime forces.