“Reports are coming in from Aleppo, Homs, Damascus and Rural Damascus, Idleb and Deir ez-Zour of mounting civilian casualties,” said UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein in a statement released by his Office (OHCHR).

“In Idleb last week, on 19 April, bombs were reportedly dropped in a vegetable market in Maarat al-Nu'man, the busiest area in town, during the busiest part of the day, killing at least 44 people and destroying dozens of shops. In the town of Kafr Nabel, bombs were again dropped on a market in the busiest area of the town, narrowly missing an after-school centre containing 50 children aged 6 to 10,” he added.

In addition, the High Commissioner said that in the opposition-controlled part of Aleppo over the past few days, pro-Government aircraft have destroyed a key hospital and other medical facilities, reportedly killing a number of medical personnel, including the only remaining paediatrician in the area, as well as many patients.

In the Government-controlled part of Aleppo, another hospital was struck and many civilians were killed in attacks launched in a number of neighbourhoods.

“In short, the violence is soaring back to the levels we saw prior to the cessation of hostilities. There are deeply disturbing reports of military build-ups indicating preparations for a lethal escalation,” Mr. Zeid said.

The High Commissioner said OHCHR has over the years documented numerous attacks on hospitals and other medical facilities as well numerous strikes on marketplaces during busy shopping times – which, depending on the circumstances, may amount to war crimes.

“In any case, these indicate a serious, alarming disregard for one of the cornerstones of international humanitarian law: the duty to protect civilians,” he said.

Civilians also remain trapped in besieged villages, towns and cities across Syria, including the town of Fu'a and Kefraya, outside the city of Aleppo. Many innocent civilians are at risk of starvation and have no access to adequate medical care, the High Commissioner said.

“The inhabitants of these towns remain at grave risk of revenge attacks by opposition groups, should truce agreements collapse,” he said.

While information is much more difficult to gather from ISIL-occupied areas, the High Commissioner expressed deep concern at the numerous allegations of civilian casualties due to air strikes.

“Urgent action is needed by all relevant actors to ensure the protection of civilians and their right to life, and to fight the impunity that has done so much to encourage the multitude of horrendous breaches of international humanitarian law and international human rights law that have taken place in Syria over the past five years,” Mr. Zeid stressed.

“In the context of such an abysmal situation, the persistent failure of the Security Council to refer the situation in Syria to the International Criminal Court is an example of the most shameful form of realpolitik,” the High Commissioner said.

“In the minds of many, the world's great powers have in effect become accomplices to the sacrifice of hundreds of thousands of human beings, and the displacement of millions. There is currently no disincentive for any of the many war criminals in Syria to stop contributing to the wild spiral of killing and destruction that has engulfed the country,” he added.

The High Commissioner also urged the international community to “address the terrible suffering of the Syrian people with the resolve that has been so absent for so long.”

“The cessation of hostilities and the Geneva talks were the only game in town, and if they are abandoned now, I dread to think how much more horror we will see in Syria,” he concluded.