Mr. Moumtzis called the lack of aid delivery approvals “really outrageous,” and the rash of attacks on medical facilities “unacceptable.”
“Humanitarian diplomacy is failing,” he said. “We are not able to reach the conscience or the ears of politicians, of decision makers, of people in power.”
Mr. Moumtzis spoke as residents of Eastern Ghouta, the cluster of Damascus suburbs under bombardment, posted the names of the dead and photographs of the children who had died. They also posted videos of the shredded bodies of small children.
Hassan Tabajo said 25 people were killed in his town alone. They included a cousin, the 10th relative Mr. Tabajo had lost in the war, who was killed when his apartment building was hit. The building also housed a center that trained women in English and tailoring; three students and a teacher died.
Also Tuesday, rebel shelling killed three people in the government-held Old City of Damascus. The attack followed two others in the past week that killed at least 10 people, including several children.
The war in Syria has displaced half the population and killed some 400,000 people, but now the carnage is growing in many places at once. The government is carrying out scorched-earth attacks in two of the last major rebel-held areas — near Damascus and in Idlib — and Turkey is striking a Kurdish area on the northern border.
“There are multiple fronts where people are under extreme danger without a view to a solution,” Mr. Moumtzis said. “We haven’t seen this.”
Russia is supposed to be monitoring a reduction in violence in both Idlib and the Damascus suburbs, where the heaviest attacks are taking place. Russia says it is trying to push Mr. Assad to negotiate with his opponents, including with some of the armed factions, although so far he has shown no inclination.
The deal to ease violence in certain areas, brokered by Russia with Turkey and Iran — as well as the rout of the Islamic State from most of its territory last year — may have given people the false impression that the Syrian war was winding down, Mr. Moumtzis said.
“There is a misperception that the de-escalation areas have resulted in peace and stability,” he said. “If anything, these have been serious escalation areas.”
Yet Syria seems to have lost its hold on public attention, even though in the past year more than 8,000 people per day have been driven from their homes. In the north since mid-December, some 300,000 people have fled from their homes, some of them displaced for the second or third time.
And more than 600 people are awaiting evacuation from the Damascus suburbs for urgent medical care, but no evacuations have been granted since 29 people were let out in November.
Mr. Moumtzis said the United Nations would “ask the government of Syria to stop besiegement,” and he condemned the lack of cooperation from some rebel groups on aid deliveries. He also pointedly cited “the failure of countries who are of influence to Damascus and others to bring the influence needed to ensure respect for human beings.”
Moaz al-Shami, an anti-government activist from the Idlib town of Saraqeb, said in an interview last week that he no longer knew why he risked his life to videotape attacks. “I don’t know what the point is,” he said.
Mr. Moumtzis contrasted the situation to the 1990s war in Bosnia, where the shelling of civilians buying bread helped galvanize international response.
“In Sarajevo we had the market massacre that woke up the conscience,” he said, but as larger death tolls in Syria receive less attention — airstrikes on marketplaces happen with some regularity — he said he wondered what level of violence it would take to shock the world into action.
“We are running out of words, to be honest, to describe it,” Mr. Moumtzis said.