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
A string of Islamic State group attacks, including suicide blasts, killed more than 150 people in southern Syria on Wednesday in one of the jihadists' deadliest assaults in months, a monitor said.
The Syrian Observatory for Human Rights said the blasts hit several areas of the largely government-held southern province of Sweida, where IS retains a presence in a northeastern desert region.
The attacks 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.
The raids began when three suicide attackers detonated their explosive belts in Sweida city as other blasts hit villages to the north and east, said the Observatory.
A fourth suicide blast hit the city later.
"IS fighters then stormed villages in the province's northeast and killed residents in their homes," said Rami Abdel Rahman, head of the Britain-based Observatory.
IS seized three of the seven villages they targeted, he said.
The suicide blasts and attacks have left at least 32 pro-government fighters and 22 civilians dead, he added, updating an earlier toll.
"The death toll rose after bodies were found in people's homes," Abdel Rahman told AFP.
At least 21 IS jihadists were also killed.
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.
State television said the army was targeting IS in the province's east, and state news agency SANA reported "army units blocked an IS attack on a number of villages in northeastern Sweida, killing a large number" of the jihadists.
SANA published images of the aftermath of the attack in Sweida city.
The remains of a victim lay sprawled on a staircase near a damaged wall, while abandoned shoes lay in the middle of the road among fruit that had spilled out of cartons.
Abdel Rahman said unidentified warplanes were also targeting IS fighters in the area.
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 regime of President Bashar al-Assad has in recent weeks ousted rebels from a majority of the country's south, part of which borders the Israeli-occupied Golan Heights.
His forces are now closing in on a patch of territory in nearby Daraa province held by jihadist group Jaish Khaled bin al-Walid, which has pledged allegiance to IS.
The group, which has around 1,000 fighters in the region, has been the target of an intense bombing campaign by Russian and Syrian jets in recent days.
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".