Assad steps up military offensive in Syria's southwest

Syrian regime forces kept up their pressure on the country's strategic southwest on Friday, using artillery, airstrikes and dropping barrel bombs that targeted rebel-held parts of the region, activists said.

The Britain-based Syrian Observatory for Human Rights said more than 12 barrel bombs hit the province of Daraa, in the first use of the rudimentary and non-discriminatory weapons there in over a year when a truce went into effect in the area.

Rockets and artillery shells have also targeted northern and eastern Daraa, and there were reports of overnight airstrikes on Busr al-Harir, a northeast Daraa town where regime troops are trying to isolate the rebels.

The regime campaign in the southwestern Syrian region bordering Jordan and the Israeli-occupied Golan Heights comes despite US warnings of "serious repercussions" for anyone violating a de-escalation agreement in place since last July.

The de-escalation zone was negotiated by Russia, the Syrian regime's main ally, Washington and Jordan.

Rebel factions, meanwhile, said they responded with missiles at a government air base in the adjacent Sweida province.

The Observatory said 16 people have been killed in government strikes since Tuesday, including nine children. At least 12,000 people have been displaced by fighting in the area since, according to the war monitor.

The agreement has been unravelling in recent weeks as the Syrian regime turned its attention southward, after seizing opposition-held areas near the capital, Damascus.

The US envoy to the UN condemned the reported cease-fire violations in a statement Friday.

"The Syrian regime's violations of the ceasefire in southwest Syria need to stop," said Ambassador Nikki Haley, adding that "Russia will ultimately bear responsibility for any further escalations in Syria."

Southwestern Syria is a mix of regime and rebel-controlled areas, with rebels controlling parts of Daraa city and areas along the border with Jordan and the occupied Golan Heights.

UN Secretary-General Antonio Guterres on Friday called for an immediate end to a military escalation in southwest Syria and a return to ceasefire arrangements agreed by Russia, the United States and Jordan.

Guterres said he was "gravely concerned" by the recent upsurge in fighting from the Syrian regime offensive, saying it posed "significant risks" to regional security.

He called for "an immediate end to the current military escalation" and urged all sides to uphold the ceasefire commitments "as a matter of priority."

The UN Security Council is scheduled to discuss Syria on Wednesday.