A senior UN official says he fears children waiting to be evacuated from a besieged rebel-held area of the Syrian capital, Damascus, are being used as bargaining chips.
UN special envoy to Syria Jan Egeland told the BBC he understood that rebels had agreed to release government workers in exchange for the children.
Another 12 patients were evacuated on Wednesday, following four on Tuesday.
Thirteen more urgent cases are expected to be evacuated on Thursday.
News of the latest evacuations from Eastern Ghouta came in a tweet from the Syrian American Medical Society (Sams).
However, a doctor with Sams, Mohamad Katoub, told the BBC that it was hard to keep up with who urgently needed to be evacuated as people continued to die.
“The last one was a girl from the list, from the 29. This morning, when the local staff reached the family to tell them that finally the approval to evacuate your little daughter arrived, the family said that our daughter died a few days ago,” he said.
About 400,000 residents in the war-torn district have been under siege by government forces since 2013.
“Let’s hope that the agreements are good when they come,” Mr Egeland told the BBC.
“There can also be bad agreements. It is a not a good agreement if they exchange sick children for detainees that means children become bargaining chips in some tug of war. That shouldn’t happen. They have a right to the evacuation and we have an obligation to evacuate them.”
The main rebel group in Eastern Ghouta, Jaysh al-Islam, said earlier on Twitter that the government had agreed to the evacuations in exchange for the release of 29 of its prisoners.
- ‘Critical point’ in Syria’s Eastern Ghouta
- Why is there a war in Syria?
Mr Egeland said those still in Eastern Ghouta had very little left in the way of medical facilities.
“The Syrian war has been a war against the medical profession in many ways,” he said.
“Too many hospitals have been bombed, have been hit on both sides, hundreds of doctors and nurses have been killed or wounded so what is left in Eastern Ghouta for the 400,000 civilians is not that much.”
Eastern Ghouta has been designated a “de-escalation zone” by the Syrian government’s main allies, Russia and Iran, along with Turkey, which backs the opposition.
But hostilities intensified six weeks ago when the Syrian military stepped up attacks in response to a rebel offensive, reportedly killing dozens of civilians.
There are also severe shortages of food, fuel and medicines, and the cold weather is threatening to worsen the hardship.
On Wednesday, the International Committee of the Red Cross (ICRC) confirmed that four critically ill people had been taken with their families to hospitals in Damascus, and that it hoped a total of 29 people would be evacuated “over the coming few days”.
“The operation is clearly a positive step that will give some respite to the people in Eastern Ghouta, especially those who are in dire need of life-saving medical treatment,” spokeswoman Anastasia Isyuk told the BBC.
“We hope this medical evacuation will only be the beginning of more to come, as there are many more people in need. It is also vital for humanitarian organisations to reach people in Eastern Ghouta with aid on a regular basis and without conditions.”
Last week, Mr Egeland said 494 people were on the priority list for medical evacuations submitted in November.
He said the number was going down, not because people were being evacuated but because people were dying.
“We have tried now every single week for many months to get medical evacuations out, and food and other supplies in.”