Jordan stepped in to try to avert further violence and stem another wave of displacement across its border with Syria on Sunday, mediating new talks between rebels and the government's main ally Russia for a truce in the southwest.

Talks in the town of Bosra al-Sham on Saturday broke down as the army seized more ground in its offensive, with insurgent lines in some areas collapsing, and a string of towns and villages accepting the return of government rule after intense bombardment.

Fighting and bombardment calmed overnight, the Syrian Observatory for Human Rights said, but reignited on Sunday around Tafas, northwest of Deraa, along with heavy air strikes.

Syrian President Bashar al-Assad's offensive in the southwest aims to reclaim one of two remaining rebel strongholds in Syria, the other being Idlib and adjacent areas in the northwest. Assad's forces captured the last enclaves near Damascus and Homs earlier this year.

Southwest Syria is a "de-escalation zone" of reduced warfare and bombardment agreed by Russia, Jordan and the United States last year. Washington warned it would respond to violations of this agreement, but has done nothing so far. Last week, rebels said the United States had told them not to expect any American military support.

The opposition's chief negotiator in wider U.N. peace talks, Nasr al-Hariri, last week accused the United States of complicity in Assad's southwest offensive, saying American silence could only be explained by "a malicious deal".

Peace talks in the town of Bosra al-Sham, home to a UNESCO world heritage site, failed on Saturday when insurgents rejected Russian terms for their surrender, but began again on Sunday under the auspices of Jordan, rebel spokesman Ibrahim al-Jabawi said.

Jordan's Foreign Minister Ayman Safadi said the kingdom was engaged in intensive diplomacy with all parties in the conflict to help broker a ceasefire that would ease plight of displaced civilians.

"We are moving in all directions and with all the parties to bring a ceasefire and protect civilians," he said in a Tweet on Saturday.

AIR STRIKES

Air strikes have pounded the region since the offensive ramped up two weeks ago, causing at least 160,000 people to flee their homes according to the United Nations.

On Saturday at least ten civilians were killed when bombs were dropped on the rebel-held village of Ghasam, relief workers said. The Observatory says more than 100 civilians have been killed since an escalation in fighting on June 19.

Many who fled have sought refuge along the borders with Jordan and the Israeli-occupied Golan Heights. Both Jordan, which already hosts more than half a million Syrian refugees, and Israel, have said their borders will stay shut.

Internally displaced boy from Deraa province stands outisde a tent near the Israeli-occupied Golan Heights in Quneitra, Syria June 30, 2018. (Photo: Reuters)

Both countries' militaries have distributed aid supplies to the people seeking shelter near the borders.

On Sunday, Israel also said it had deployed more tanks and artillery to the Syrian front as a precaution because of the fighting there.

An Israeli army commander told Reuters that it was hard to quantify how many people had sought shelter in the area immediately across the border, but that it was in the thousands and there were hundreds more arriving each day.

Southwest Syria was an early hotbed of the uprising against Assad in 2011 that morphed into the seven-year conflict that has cost over half a million lives and pushed half the country's pre-war population from their homes.

Until Assad's offensive began this month, its front lines had been mostly stable. However, the army has now taken much of the eastern side of the rebel territory there and forced two large towns on the western side, Dael and Ibta, to accept deals to come back under state rule.

That pattern of local groups in towns and villages agreeing deals with the government independently of the main rebel factions has been repeated in locations across the southwest.