Syrian rebels have agreed to resume talks on a truce with the government in the country’s south-west, after a day of intense air and artillery strikes.
Pro-government and Russian forces stepped up their bombardment of rebel towns in Deraa province on Wednesday when their demands were rejected.
On Thursday, the rebels said they would return to the negotiating table.
At least 320,000 people have fled their homes since the government launched an offensive in the region two weeks ago.
Many of the displaced are stranded in makeshift camps along the borders with Jordan and the Israeli-occupied Golan Heights. Both countries have refused to allow large influxes of refugees, sparking fears of a humanitarian crisis.
Almost 150 civilians are also said to have been killed in the fighting.
Deraa and neighbouring province of Quneitra had been relatively calm for almost a year because of a “de-escalation” agreement brokered by the US and Jordan, which support the opposition, and Russia, a staunch ally of the government.
But Syrian President Bashar al-Assad set his sights on regaining full control of the south-west after defeating rebels in the Eastern Ghouta region outside Damascus in April.
The Syrian army and allied militias have made significant gains since launching the offensive in the region on 19 June with the support of Russian aircraft.
More than 30 rebel-held towns have negotiated individual surrender deals, but talks between rebel factions and Russian mediators about a wider ceasefire reportedly collapsed on Wednesday.
Russia had demanded that the rebels immediately hand over all their heavy weapons and accept the return of state institutions in return for guarantees of safety, rebel sources said. Rebel commanders wanted to hand over weapons in phases and to be given safe passage to rebel-held northern Syria, they added.
The Syrian and Russian militaries responded by carrying out more than 2,350 air and artillery strikes in the next 23 hours, according to the Syrian Observatory for Human Rights.
The UK-based monitoring group said a mother and her four children were among six people killed in Saida, a town about 10km (6 miles) north of the Jordanian border.
An AFP news agency journalist in Deraa city reported that the air strikes on rebel-held southern districts were the most intense since the start of the offensive.
On Thursday evening, opposition spokesman Ibrahim al-Jabawi announced that Jordanian mediators had persuaded rebel leaders to agree to an immediate cessation of hostilities and resume negotiations on a deal to end the fighting.
The deputy leader of the rebels’ negotiating committee, Khaled al-Mahamid, said Russia had backed down on several conditions.
The UN Refugee Agency said that up to 325,000 civilians had been displaced. About 59,000 of them are at camps close to the Nassib border crossing with Jordan, 48,500 at the Tal Shihab crossing, and 189,000 at camps and villages in Quneitra province, close to the occupied Golan Heights. Some 8,500 others are displaced elsewhere in Deraa province.
UN High Commissioner for Refugees Filippo Grandi described the conditions at the camps as “dire and insecure”, with people lacking shelter, regular access to clean drinking water and healthcare. They are also subject to dusty desert winds and high temperatures of up to 45C (113F).
Local sources told the UN on Monday that 12 children, two women and one elderly man had died as a result of scorpion bites, dehydration and diseases transmitted through contaminated water.
Mr Grandi urged Jordan to open its border crossings to Syrians seeking safety.
“Given the immediate dangers, I am advocating for granting temporary refuge in Jordan to those in need of safety and for the international community to provide immediate and substantive support to Jordan, in a spirit of solidarity and responsibility sharing,” he said.
“Thousands of innocent lives are going to be lost, once again, if urgent action is not taken,” he warned.
Jordan’s government rejected the request, saying it was the UN’s responsibility to provide people with safe havens inside Syria.
The kingdom has also said its financial resources and infrastructure are already strained by hosting close to 1.3 million Syrians who have arrived since the civil war began in 2011, including 666,000 refugees registered with the UN.