Rebel shellfire slammed into the southern Syrian city of Sweida on Tuesday for the first time in three years, a monitor said, as fresh regime reinforcements arrived in the area.
The government holds most of Sweida province but rebels still control much of the nearby Daraa and Quneitra governorates.
On Tuesday, the Syrian Observatory for Human Rights said opposition forces fired shells into Sweida city, "which led to loud blasts but no casualties."
"It is the first time since 2015 that the city has been subjected to shellfire," said Observatory chief Rami Abdel Rahman.
Syrian state news agency SANA also blamed rebels "spread out in the towns and villages in eastern parts of Daraa province" for firing shells on Sweida.
Sweida, whose residents are mostly from the Druze minority, has remained relatively insulated from seven years of war that ravaged the rest of the country.
But rebels hold a sliver of territory in western Sweida that borders their main bastion in the province of Daraa, and clashes and exchanges of fire have erupted in that area in recent days.
Syria's government has set its sights on ousting rebels from the south and has been dispatching troops and equipment there for weeks.
On Tuesday, they dropped new flyers on the rebel-held half of Daraa city, calling on residents to expel rebels, "like your brothers did in Eastern Ghouta and Qalamun," referring to two areas near Damascus recently recaptured from the opposition.
Rebels appeared to fear the regime would use Sweida's civilian population as justification for the assault, and issued a message addressed to them on Tuesday.
"We call on our people in Sweida province not to serve as bait for the goals of the regime, sectarian militias from Iran, and Hezbollah, which are trying to occupy this land and divide its people," they said in a statement.
But the government has also hinted that a political settlement over the south's fate could be reached.
"We have moved towards the south and we are giving the political process a chance," Syrian President Bashar al-Assad said last week.
"If that doesn't succeed, we have no other option but to liberate it by force."