BEIRUT — A string of suicide blasts and raids claimed by the Islamic State group killed more than 220 people in southern Syria on Wednesday, in one of the jihadists’ deadliest ever assaults in the country.

The Syrian Observatory for Human Rights said the attacks hit several areas of the largely government-held southern province of Sweida, where IS retains a presence in a northeastern desert region.

The bloodshed came almost a week into a Russia-backed regime campaign to oust IS fighters from a holdout in a neighbouring province of the country’s south.

IS claimed responsibility for the violence, saying "soldiers of the caliphate" attacked Syrian government positions and security outposts in Sweida city, then detonated explosive belts.

The Britain-based Observatory said four suicide bombers targeted Sweida city while others hit small villages to the north and east and shot residents in their homes.

At least 221 people were killed, including 127 civilians, the Observatory said.

The remaining 94 dead were pro-regime fighters, mostly residents who took up arms to defend their homes, it said.

The overwhelming majority of the dead "were in (Sweida’s) northern countryside, where the bodies of civilians executed inside their homes were found," Observatory head Rami Abdel Rahman said.

Sweida, whose residents are mostly from the Druze minority, has been relatively insulated from the war that has ravaged the rest of the country since 2011.

"It’s the bloodiest death toll in Sweida province since the start of the war" and one of the deadliest ever IS attacks in Syria, the Observatory chief said.

He said regime forces eventually ousted IS from several villages its fighters had seized and put an end to the attacks.

"Some residents who fled the attacks on their villages are returning and finding people dead in their homes," Abdel Rahman said.

At least 38 IS fighters were also killed, including the suicide attackers.

State media confirmed the attacks had killed and wounded people in Sweida city and villages to the north and east but did not give a specific toll.

"Today’s crime shows that countries supporting terrorism are trying to breathe life back into the terrorist organisation to keep it as a card in their hand that they will use to achieve political gains," Syrian President Bashar al-Assad as he received Russia’s envoy to Syria Alexander Lavrentiev.

"These attempts will only succeed in... shedding more innocent blood," he added, in comments carried on his social media accounts.

The UN’s humanitarian coordinator in Syria Ali al-Zaatari condemned the "terrorist bombing in Sweida city", saying all civilians should be protected.

Government ally Russia said the IS attacks "confirm the need for energetic and coordinated efforts by the international community to eradicate this universal evil from Syrian territory". — AFP