The latest air strikes killed more than 12 people in Eastern Ghouta, a pocket of towns and farmland east of Damascus where the death toll has climbed to more than 230 in the last four days - the enclave's deadliest week since 2015, according to the Syrian Observatory for Human Rights.
Syrian warplanes and artillery have battered the enclave's towns since Monday, trapping thousands of families in makeshift bomb shelters and overwhelming rescue workers.
The UN Security Council is considering a draft resolution demanding a 30-day ceasefire in Syria to allow for urgent deliveries of humanitarian aid.
But around mid-morning, an announcement blasted over mosque minarets warned of incoming strikes: "Surveillance plane in the sky. One is that we don't get approvals to actually go but even if we got approvals, there just is too much fighting going on", he said, pointing to hostilities in Idlib, Eastern Ghouta, and Afrin.
Ankara announced Thursday it would host a new three-way summit to revive efforts to end the war, which has killed at least 340,000 people and displaced millions since 2011.
Syrian activists say the death toll from airstrikes and shelling of eastern suburbs of the capital Damascus has risen to at least 56.
Eastern Ghouta has an estimated 400,000 residents, who are also trapped by a tightening government siege and critical shortage of medical supplies and food. "The siege means there is nowhere for them to escape", said Sonia Khush, Save the Children's Syria response director.
Care International said the intensity of the air strikes had made it extremely hard for relief workers to assist the needy.
"If there is no ceasefire, if this is all left unheard, we can not imagine the scale of the humanitarian disaster", she said.
Eastern Ghouta was one of several so-called de-escalation zones agreed a year ago by three of the main outside players in the conflict - Turkey, Iran and Russian Federation.
But the Security Council on Thursday failed to support the proposal, with long-time regime ally Moscow dismissing it as "not realistic".
The Russian military says a USA strike on government-backed troops in eastern Syria reflects Washington's efforts to make a grab for the nation's economic assets.
Violence also flared in eastern Syria, where the US-led coalition said it killed at least 100 pro-regime fighters to fend off an attack on its Kurdish allies.
US Defence Secretary Jim Mattis said the coalition acted in self-defence after pro-Damascus forces moved on an area under the control of the US-backed Syrian Democratic Forces.
Turkey's state-run news agency says authorities have issued detention warrants against the co-leader of the country's pro-Kurdish party and 16 other activists for speaking out against Turkey's military offensive in northern Syria.
The Russian officials offered assurances that they would not engage the coalition forces in the area, Veale said.
The operation is being carried out under the framework of Turkey's rights based on worldwide law, UN Security Council's decisions, self-defense rights under the UN charter and respect for Syria's territorial integrity, it said.
Wounded fighters were taken to the military hospital in the government-controlled eastern city of Deir Ezzor.
Morgan out, England bat first
But selectors have opted to stick with the bowling attack that orchestrated a stunning England collapse of 7-43. Australian opener Aaron Finch was cleared to return from a hamstring injury, with Travis Head out of the side.