Explosions in weapons and fuel depots at a Syrian regime military air base in central Syria left at least 11 pro-regime fighters dead on Friday.
The Britain-based Syrian Observatory for Human Rights said the blasts took place at Hama military airport.
"They were probably caused by a technical problem," said Observatory director Rami Abdel Rahman.
Eleven regime forces were killed, including members of allied militias, and dozens more wounded or still unaccounted for, he added.
“Five blasts at least were heard inside Hama military airport ... targeting ammunition and fuel depots,” the Observatory added.
Official Syrian state media also reported massive explosions heard near the Hama airbase but did not provide any details.
Tensions are high in Syria after several Israeli bombing raids in recent weeks on regime positions, as well as on military installations reportedly used by regime ally Iran.
The latest wave came in the early hours of May 10, when Israel carried out dozens of raids against what it said were "Iranian" targets in Syria.
It has repeatedly threatened to act if Iran developed an entrenched military presence in southern Syria, which borders the Israeli-occupied Golan Heights.
More than 350,000 people have been killed since Syria's conflict erupted in March 2011 with protests that have since spiraled into a brutal war.
