BEIRUT - 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. 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.

It also said one girl was killed and two people were wounded in opposition fire on government-held parts of Daraa city. 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. Rebel commander Abu Hassan told AFP on Tuesday his units had seen the reinforcements and were on high alert. "We are almost always mobilised. The joint operations room has upped its coordination to the highest level," he said.

On Tuesday, the regime 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. Opposition fighters 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 a political settlement could be reached over the south's fate. "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."

Assad has regained the upper hand since 2011, when protests erupted across the country demanding he step down. Demonstrations then turned into an armed conflict that has killed more than 350,000 people, drawn in world powers, and given rise to jihadists like the Islamic State group.

IS has been defeated across much of Syria but the jihadists hold a few positions in desert areas of Sweida, where it has clashed with government troops recently. On Tuesday, eight regime forces were killed in clashes with IS in the area.