BEIRUT — As the U.N. Security Council voted unanimously Saturday on a 30-day cease-fire to stem spiraling bloodshed in Syria, medics in hospitals across a besieged Damascus enclave said they were treating fresh wounds and waiting for a miracle.

More than 500 people have been killed and 2,500 wounded in a ferocious six-day blitz by Syrian and Russian warplanes on the opposition-held suburb of Eastern Ghouta, according to relief groups and rescue workers. World powers have scrambled to stem the violence, one of the bloodiest periods of Syria’s six year war, behind closed doors and in charged public meetings at the U.N. Security Council. 

Jaded after successive failed cease-fires, doctors reached by phone Saturday said they were wary of raising patients’ hopes and that shelling continued. 

“The last explosion I heard was five minutes ago. I hope this vote will succeed, but we do not trust Russia,” said Hamza Hassan, a doctor supported by the Syrian-American Medical Society, a nonprofit group. “We are so exhausted. So exhausted.”

U.S. and European officials blamed Russia, a key ally of Syrian President Bashar al-Assad, for delaying the vote for two days as Eastern Ghouta’s casualty count soared. 

“Here we are voting for a cease-fire that could have saved lives days ago. In all this time, nothing has changed in the resolution, aside from a few comments,” said Nikki Haley, the council’s U.S. representative. 

Stephen Hickey, representing the United Kingdom, said the council argued “over commas” as Syrian warplanes bombed civilians in their hospitals and homes.

Since Saturday, the attacks appeared to target dozens of medical facilities, many of them already buckling under the strain of a five-year siege by Syrian government forces. On Saturday, Doctors Without Borders said that the latest bombardment had left Eastern Ghouta’s health network “in its final throes.”

Huddled in a single room days earlier, Hassan’s colleagues and patients had waited for hours as bombs fell and the most grievously wounded died unattended.

The doctors said the bombardment by forces loyal to Assad was worse than anything they had seen in six years of war. For Hassan, on duty that day, it was the first time that he looked at the scared faces in his hospital and knew that many would soon be dead. 

His colleagues said they were faced with an impossible task. The blood bags were depleted. So was the anesthetic. In the corner, medics were gathered around a young man whose skull was hanging open, one of them providing manual respiration, another just holding his hand.

“We were so afraid that we would all die there together,” Hassan said. “I told those who could to scatter for their safety. It was an impossible decision.”

There is no set time for the cease-fire to take effect, but the resolution demands that it be followed immediately by access for humanitarian convoys and medical teams to evacuate the critically ill and wounded.

But there is one exemption, which may yet pave the way for an even fiercer assault on the battered enclave. The resolution said that attacks directed at extremists from the Islamic State group and all al-Qaeda affiliates will be allowed to continue. Several hundred of Eastern Ghouta’s fighters are linked to the country’s al-Qaeda affiliate, Hay’at Tahrir al-Sham, although most are not.

The Washington Post spoke to people inside a heavily bombarded suburb of Damascus, Syria. Almost 300 civilians are dead since intense airstrikes began Feb. 18.

The area’s rebel forces also have continued to retaliate during previous cease-fires, shelling densely populated residential areas in Damascus.

In a statement, Amnesty International called Saturday’s vote a “step in the right direction” but warned that the “long list of legitimate targets leaves too much room for warring parties to justify their indiscriminate attacks against civilians and civilian infrastructure.”

After six years of bitter conflict, the violence of the past week underscored the likelihood of deepening bloodshed in the coming months. Pro-government forces have been intensifying attacks on the country’s final opposition-held areas, and hopes that international efforts would stem the violence have dimmed.

Diplomats and aid groups have warned that hundreds of thousands of civilians are caught in the middle of a dizzying array of warring parties, and many more are likely to die before the conflict is out. 

“Three days ago, medical staff in [Eastern Ghouta] were calling for supplies. Now they are telling us that even if they had those supplies they couldn’t do anything. There are too many patients,” said Meinie Nicolai, the director of Doctors Without Borders’ Brussels office.

The pace of violence and paucity of resources had forced doctors to choose who lived and died. “When there’s a bombing near the hospital, the floodgates open and we can only focus on the cases with the greatest chances of survival,” said Amani Ballour, a medic in one of the enclave’s hospitals. “There was a child with his brain hanging out and the mother was begging me to help. We had to let him die.”

As staff and patients prepared to move from Hassan’s hospital Wednesday, medics said that one of the nurses, 19-year old Bushra Obeid, was overcome by fear. “She was too scared for her son, so she ran,” said Hassan. “Then the bombs targeted the place where they took shelter. We didn’t find them in the rubble until midnight.”

Zakaria Zakaria reported from Istanbul.