Explosions rocked weapons and fuel depots at a regime military airbase in central Syria Friday, a monitor said, adding that the cause of the blasts was not yet clear.

"The explosions struck several regime depots of weapons and fuel at Hama military airport," Rami Abdel Rahman, the head of the Syrian Observatory for Human Rights, said.

Official Syrian state media also reported massive explosions near Hama and pictures posted on social media showed a huge plume of gray smoke billowing into the sky.

Amid speculation of another Israeli strike against military targets in Syria, Abdel Rahman said it was not yet clear what caused the blasts.

Israel has carried out several air strikes against Iranian targets in Syria in recent weeks, with the latest wave coming a week ago and bringing the region closer to a major flare-up.

In late April, a missile attack on regime outposts in northern Syria killed more than a dozen pro-Assad fighters, many of them Iranians.

Iran is one of the Syrian regime's key allies and has forces positioned across the country.