At least 215 people have died in a series of apparently co-ordinated attacks in south-western Syria, local officials and a monitoring group say.
Several suicide bombings struck in and around the government-held city of Suweida - the main city in the province - on Wednesday.
The Islamic State group (IS) said it carried out the attacks.
Pro-government forces were later reported to be engaged in gun battles with IS militants east of the city.
The Syrian government, backed by Russia, recently launched a campaign to retake the remaining rebel-held areas across the south of the country.
Wednesday's wave of attacks was the deadliest on government-held territory in months, correspondents say.
The Syrian Observatory for Human Rights, a UK-based monitoring group, reported a string of suicide blasts in Suweida, south of the capital Damascus, and in villages to the north and east. It said militants also stormed homes in the villages and killed the occupants.
It said at least 221 people had been killed, 127 of them civilians.
"It's the bloodiest death toll in Suweida province since the start of the war [in 2011]," observatory head Rami Abdel Rahman told AFP news agency.
The Suweida health authority told pro-government radio station Sham FM that 215 people had been killed and 180 injured.
State news agency Sana earlier reported one suicide attack at a market in Suweida and said security forces had killed two other attackers before they could blow themselves up. Militants also attacked three villages north-east of the city, it said.
State TV also said government forces were "targeting positions of the Daesh [IS] terrorist group" in countryside to the east of Suweida.
Suweida governor Amer al-Eshi told state-run Ikhbariyah TV that the city was now "secure and calm".
Over the past year, IS has lost most of the land it once held across Syria and neighbouring Iraq.
At the peak of its power, around 10 million people lived in IS-controlled areas, but the US military said earlier this year that the jihadist group had been ousted from 98% of its former territory.
In Syria, the group is still present in small pockets in the southern provinces of Suweida and Deraa, as well as parts of the country's east.
What is happening elsewhere in the country?
The Syrian military, backed by Russian forces, recently launched an operation to drive rebels from their remaining strongholds in the south-west.
On Wednesday, Russia-backed government forces were also reported to be bombarding pockets of IS-held territory in Deraa, west of Suweida.
At least 270,000 people have fled their homes in the region as fighting continues, the UN says.
On Sunday, Israel allowed the evacuation of hundreds of White Helmets civil defence workers who were trapped in a war zone in southern Syria.
The Syrian government condemned the move, describing it as a "criminal operation" by Israel and others.