A string of suicide blasts and raids claimed by the Islamic State group killed more than 150 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.
They came almost a week into a deadly 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 their explosive belts.
The Britain-based Observatory said three suicide attackers set off booby-trapped belts in Sweida city, as other blasts hit villages to the north and east. A fourth suicide explosion hit the city later.
"IS fighters then stormed villages in the province's northeast and killed residents in their homes," Observatory head Rami Abdel Rahman said.
The suicide blasts and raids killed 156 people including 62 civilians, the Observatory said.
The remaining 94 dead were pro-regime fighters, most of whom where residents who had picked up weapons to defend their villages, it said.
Sweida, whose residents are mostly from the Druze minority, have 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" in 2011 and one of the deadliest ever in Syria, Abdel Rahman said.
The violence also left 30 IS fighters dead, including the suicide attackers.
The jihadists captured at least three of the seven villages it targeted but clashes were ongoing today, the Observatory said.
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.
SANA published images of the attack's aftermath in Sweida city, showing the remains of a victim sprawled on a staircase near a damaged wall.
Abandoned shoes lay in the middle of the road among fruit that had spilled out of cartons.
The UN's humanitarian coordinator in Syria Ali al-Zaatari condemned the "terrorist bombing in Sweida city today," saying all civilians should be protected.
And the Russian foreign ministry said the IS attacks "confirm the need for energetic and coordinated efforts by the international community to eradicate this universal evil from Syrian territory".
State television said the army was targeting IS in the province's east.
Despite pro-government forces ousting the group from urban centres in eastern Syria last year, surprise IS raids in recent months have killed dozens of regime and allied fighters.
The jihadists still hold some territory in Syria's south, including in Sweida and another isolated but larger patch in neighbouring Daraa province, to the west.
That pocket is held by Jaish Khaled bin al-Walid, a jihadist faction whose 1,000 fighters have pledged allegiance to IS.
After ousting non-jihadist rebels from most of the country's south, President Bashar al-Assad's troops and his Russian allies are now closing in on the IS pocket in Daraa province.
SANA said the IS attacks on neighbouring Sweida were an attempt to relieve pressure "on IS remnants facing their inevitable end in the western Daraa countryside".
Today, Russia-backed regime forces pressed their heavy bombardment of the IS-held pocket in Daraa.
At least 41 civilians have been killed in air strikes on the jihadist holdout since July 19, the monitor says.
Fierce clashes between the two sides have killed 49 regime fighters and 67 jihadists.
Syria's south is ostensibly protected from fighting by an internationally brokered ceasefire since last year, but violence has dramatically risen in recent weeks.
Last month, Assad launched a lightning assault that battered rebel areas in the south and brought most of Daraa province under his control.
He then moved onto Quneitra, the neighbouring province which borders the Israeli-annexed Golan Heights.
Yesterday, a Syrian military source accused Israel of firing at one of its warplanes as it carried out operations against jihadists in Quneitra.
Israel's army earlier said it had shot down a Syrian fighter jet that had infiltrated Israeli airspace, risking another escalation around the sensitive buffer zone.
The Damascus regime has long accused Israel of backing IS and other anti-government factions.
IS overran large parts of Syria and neighbouring Iraq in 2014, but has since lost most of that territory.
More than 350,000 people have been killed and millions displaced since Syria's war started in 2011 with the brutal repression of anti-government protests.