Israeli raids targeting arms depots and military positions in eastern Syria killed 57 regime loyalists, in the deadliest such strikes since the start of the conflict, a monitor said on Wednesday.

The Israeli air force carried out more than 18 strikes against multiple targets in an area stretching from the eastern town of Deir Ezzor to the Iraqi border, the Syrian Observatory for Human Rights said.

At least 14 Syrian regime forces, 16 Iraqi militia fighters, and 11 Afghan members of the pro-Iran Fatimid Brigade were among those killed, the Britain-based monitoring group said. At least 37 others were wounded.

Paramilitaries belonging to the Lebanese Hezbollah movement and the Fatimid Brigade, which is made up of pro-Iranian Afghan fighters, operate in the region, the Observatory said.

Days before the strikes, the Fatimid Brigade transported a consignment of Iranian-manufactured weapons to eastern Syria from neighbouring Iraq.

They were stored in the region targeted on Wednesday, the monitor said. The Israeli military did not immediately comment.

In June 2018, strikes on the same region had killed at least 55 pro-government fighters, including Iraqis as well as Syrians.

The latest raids came hours after separate strikes near the Iraqi border killed at least 12 Iran-backed militia fighters on Tuesday.

The Observatory said it could not identify the warplanes responsible for the earlier strikes.

The Syrian state news agency SANA reported Wednesday's raids but gave few details.

“At 1:10am (2310 GMT Tuesday), the Israeli enemy carried out an aerial assault on the town of Deir Ezzor and the Albu Kamal region,” SANA said, citing a military source.

“The results of the aggression are currently being verified,” it added.

It is less than a week since the last wave of Israeli strikes in Syria.

On January 7, Israel targeted positions in the south and in the southern outskirts of Damascus, killing three pro-Iran fighters.

Israel routinely carries out raids in Syria, mostly against targets linked to Iran in what it says is a bid to prevent its arch foe from consolidating a foothold on its northern border.

Observers have warned that Donald Trump and Israel could up the ante against Iran and its regional allies in the dying days of the US president's tenure.

Israel hit around 50 targets in Syria in 2020, according to an annual report released by the Israeli military.

It has carried out hundreds of air and missile strikes on Syria since civil war broke out in 2011, targeting Iranian and Lebanese Hezbollah forces as well as Syrian government troops.

Israel rarely acknowledges individual strikes but has done so when responding to what it describes as aggression inside Israeli territory.

The war in Syria has killed more than 380,000 people and displaced millions more since it erupted after the brutal repression of anti-government protests.