With Russia's help, Syrian President Bashar al-Assad's army has battered Daraa province for over a week with air strikes, rocket fire and crude barrel bombs.
Talks to end the Syrian government's offensive on Deraa province collapsed on Saturday after rebels rejected a demand to surrender by regime ally Russian Federation.
Discussions on Sunday were hard, said diplomatic sources familiar with the talks.
After talks with Moscow, a wave of rebel areas in the south agreed in recent days to a government takeover in exchange for an end to almost two weeks of ferocious air strikes and barrel bombing.
The Syrian Observatory for Human Rights, a UK-based war monitoring group, said the campaign had killed at least 98 civilians since June 19.
Losing Busra al-Sham, a major town near the provincial capital of Daraa, would be a significant loss for the opposition in the teeth of a Russian-backed Syrian army offensive in the southwest that has taken chunks of rebel territory.
Washington has told rebels not to expect military support against the assault.
Syrian state media said earlier Saturday that more areas in Daraa province had been captured and in others rebels had agreed to hand over their weapons and reconcile with the government.
Air raids continued in the meantime, said the Syrian Observatory for Human Rights, in an offensive that the United Nations says has driven 160,000 people from their homes, threatening a humanitarian catastrophe.
The Syrian government pressed ahead with its offensive to reclaim the strategic region that extends along the border with Jordan and the Golan Heights, and which was until recently part of a USA -backed and negotiated truce.
Syrian rebels meeting Russian officers in a southern Syrian town on Saturday said negotiations for a peace deal with the government ended in failure after they rejected Moscow's demands to surrender, their spokesman said, cited by Reuters."The meeting ended in failure".
Both countries' militaries have distributed aid supplies to people seeking shelter near the borders.
Jordan said Sunday it would be unable to host a new wave of Syrian refugees and that the border would remain closed, as Damascus escalated its bombardment on the southwestern region bordering the kingdom and the Israeli-annexed Golan Heights.
More than 350,000 people have been killed in Syria since the country's war started in 2011 with the brutal repression of anti-government protests. Until Assad's offensive began this month, its front lines had been mostly stable.
This video here was shared by a local activist group from Daraa.
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