Syrian government offensive advances across country's southwest

Syrian government forces pounded rebel-held areas of the southwest with artillery on Thursday, in a steady escalation by President Bashar al-Assad, who has vowed to win back the area bordering Jordan and the Israeli-occupied Golan Heights.

The Syrian Observatory for Human Rights said 12,500 civilians had fled the town of Busra al-Harir and nearby areas of Daraa province in the past two days. Rebel officials gave conflicting assessments of the scale of displacement.

The United States has warned it would take "firm and appropriate measures" in response to government violations of a "de-escalation" deal it brokered with Russia last year to contain the conflict in the southwest.

The conflict has pivoted towards the country’s southwest since the Syrian government, with help from Russian and Iran-backed allies, crushed the last remaining pockets of rebel-held territory near Damascus and the city of Homs.

A military campaign to recover the area may be complicated by the interests of both US-allied Jordan and Israel, which has expressed alarm at Iran's role in Syria.

The US State Department said it was "deeply troubled by reports of increasing Syrian regime operations" in the area.

"Syrian regime military and militia units, according to our reports, have violated the southwest de-escalation zone and initiated air strikes, artillery, and rocket attacks," spokeswoman Heather Nauert said in a statement, warning the Russian and Syrian governments of "serious repercussions" for the violations.

While Syrian government forces have deployed artillery in the attacks so far, there have been few air strikes. Air power has been critical in helping the government defeat rebels in places such as Aleppo and Eastern Ghouta.

The Syrian state news agency SANA said the army was carrying out "focused artillery strikes" on militant positions in the towns of al-Harak and Busra al-Harir. State media said rockets fired by rebels from the Daraa area had killed two people in the government-held city of Sweida to the east.

Nassim Abu Arra, commander of the rebel group Youth of Sunna Forces, said he believed government forces were vying to capture Busra al-Harir and the surrounding area, where shelling had escalated.

Abu Bakr al-Hassan, spokesman for another southern rebel group Jaish al-Thawra, described the shelling in that area as heavy. "The civilians are afraid that the random bombardment is the start of a campaign the regime and the Iranian militias have been planning to launch in the south," he told Reuters.

The UN was "concerned about reports of an escalation of violence in Daraa governorate", which was "endangering civilians and displacing hundreds of families", said Jens Laerke, a spokesperson for the UN's Office for the Coordination of Humanitarian Affairs.

Assad said earlier this month that the government, at Russia’s suggestion, was seeking to strike a deal in the southwest similar to agreements that have restored its control of other areas through withdrawals of rebel forces.