United Nations — UN Secretary-General Antonio Guterres 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 government 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 European Union also warned of “devastating humanitarian consequences” in rebel-held southern Syria.

The EU's diplomatic arm called for protecting civilians and allowing humanitarian access to Daraa province where it said the Assad regime, backed by Russia and Iran, has started an offensive.

US Ambassador Nikki Haley separately urged Russia to pressure its Syrian ally to uphold the truce.

Syrian regime forces on Saturday made their first gains on the ground against rebel fighters in the southern province of Daraa after several days of intensified bombardment, a monitor said.

Since Tuesday, regime troops have been ramping up shelling on opposition-held areas in Daraa’s eastern countryside ahead of an apparent military offensive against rebels there.

“Regime troops made their first advance in the area since the military escalation on Tuesday, seizing the villages of Al-Bustan and Al-Shumariya in the eastern part of Daraa province,” said the Syrian Observatory for Human Rights.

The shelling and clashes are currently focused on a wedge of rebel territory between Daraa’s eastern countryside and the western part of the neighboring province of Sweida.

The army seems to want to split that wedge into a northern and southern section, Observatory head Rami Abdel Rahman said, “to facilitate their operations and increase the pressure on rebel factions, allowing it to advance more quickly.”

Artillery and air strikes “are causing the civilian population to flee towards the border with Jordan and with potentially devastating humanitarian consequences,” an EU spokesperson warned.

The statement quoted the United Nations as saying the attacks endangered more than 750,000 civilians in the area that borders Jordan and the Israeli-occupied Golan Heights.

It said the assault was taking place in a “de-escalation zone” that is supposed to be protected by the guarantors of the Astana peace talks.

“The Astana guarantors are bound to ensure cessation of hostilities in these zones as a matter of priority and they are expected to deliver on this commitment,” the External Action Service said.

“All necessary measures to protect civilian lives as well as unhindered, safe and sustainable humanitarian access need to be ensured,” it added.

Daraa, Quneitra and Sweida are included in a “de-escalation zone” agreed by the United States, Russia and neighbor Jordan last year. — Agencies