An Iranian Revolutionary Guards official denied on Thursday that recent Israeli strikes on eastern Syria led to any deaths, the Fars news agency reported.

"This attack caused no human losses," Ahad Karimkhani, deputy political head of the Guards' foreign operations arm, the Quds Force, was quoted as saying.

The "attacks that [Israeli forces] carry out under different pretexts are blind and with no strategic goals", Karimkhani said.

He vowed that attacks on "resistance axis positions in Syria will certainly face a serious and severe response".

Syria's state news agency SANA said on Wednesday that the "Israeli enemy carried out an aerial assault on the town of Deir Ezzor and the Albu Kamal region," without giving further details.

A Britain-based war monitoring group said the air strikes killed 57 people, including Iran-backed fighters.

The overnight raids targeted arms depots and military positions and were the deadliest such strikes since the start of the Syrian conflict, the Syrian Observatory for Human Rights said.

Iran has been a staunch supporter of Syrian President Bashar Assad in the civil war that has ravaged the country since 2011.

Israel has carried out hundreds of air and missile strikes on Syria since the war broke out, most of them against what it says are Iranian-linked targets.

The conflict has killed more than 387,000 people and displaced more than half of Syria's pre-war population.