Syrian forces, backed by intense air bombardment, have gained territory on the edge of Douma - the last rebel pocket in Eastern Ghouta near the capital Damascus.
The regime has used a combination of fierce bombardment and two negotiated withdrawals to empty out 95 percent of the enclave but rebels are still entrenched in the largest town of Douma.
Speaking on Friday, Stephane Dujarric, spokesperson for the United Nations, said the renewed outbreak of fighting in Douma "is of great concern to us".
"The bombing still hasnt stopped".
Firas al-Doumi, a rescue worker inside the battered town, told AFP military planes and helicopters were circling overhead.
According to the Syrian Civil Defence, a group of rescuers operating in opposition-held areas in Syria, the air raids killed at least 30 civilians, including women and children.
More than 1,600 civilians were left dead and thousands more wounded in eastern Ghouta since February 18, the Observatory stated earlier.
"There are still a number of people who are besieged and trapped in the area", he told reporters at the United Nations headquarters in New York, "We remind all parties that it is a violation of worldwide law to target civilian infrastructure, to target civilians".
Top Jaish al-Islam political figure Mohammad Alloush yesterday blamed global supporters of Syria's government for hamstringing the talks.
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Assad's forces and Jaish al-Islam began negotiations ten days ago.
According to local sources, Friday's airstrikes were prompted by a disagreement between Russian Federation and the Jaish al-Islam, with the latter insisting that Duma be included in the evacuation process.
"All of a sudden, with no warning, the shelling starts".
It remains unclear exactly why the talks fell apart this week. "There were 20 strikes in 15 minutes", Mohammed, a medic, told AFP.
Moscow announced a deal with Jaish al-Islam last Sunday, ushering in three consecutive days of evacuations from Douma that saw almost 3,000 fighters and civilians bussed to northern Syria.
"The talks were going well", he said, but power struggles between the regimes allies had caused them to break down. Fighters and civilians with familial ties to the group are being rejected, residents said.An activist interviewed Friday said the choice to stay had not been his own, after Jaish al-Islam declined to clear two of his relatives to leave and held up his application as a result.
The wounded were being brought in with fractures and other injuries, and there had been three amputations on Friday alone, he said.
On Saturday, fresh artillery fire hit those fields, said the Observatory.
Observatory head Rami Abdel Rahman said dozens of people had been injured and the army launched a ground offensive on its outskirts after talks sputtered over a rebel withdrawal.