Geneva - UN investigators on Tuesday urged all sides in Syria's bloody war to breath new life into a faltering ceasefire, even as Washington and Moscow failed to agree a deal to stem the violence.
The UN Commission of Inquiry on Syria said a cessation of hostilities agreed in February had finally offered "a glimmer of hope" to civilians who have endured five-and-a-half years of horrific violence.
But it pointed out that just a month later, fighting and indiscriminate attacks on civilian areas, including numerous hospitals, had surged.
"The cessation of hostilities agreement brought a welcome respite for civilians that lasted all too briefly," the commission said in its 12th report, covering the period from January to July 2016.
The three-member team emphasised the need to restore the ceasefire, insisting that "the sense of hope engendered earlier this year must be revitalised."
And it urged more support for UN Syria envoy Staffan de Mistura, who is struggling to get the stalled talks back on track.
The report was published after US President Barack Obama and Russian counterpart Vladimir Putin met for talks on Syria on the sidelines of a G20 meeting in China this week, which were described "productive".
But the two powers failed to produce an expected deal to ease the violence in Syria, where more than 290 000 people have been killed and more than half the population displaced since March 2011.
The UN commission, headed by Brazilian Paulo Sergio Pinheiro, has repeatedly accused the various sides of a wide range of war crimes and in some cases crimes against humanity.
The investigators on Tuesday reiterated their call for the Security Council to refer the situation in Syria to the International Criminal Court.
That remains a very unlikely scenario, however, since Security Council member Russia remains intent on supporting its ally in Damascus.
In their report, they said that "unlawful killings, including deaths in detention, and summary executions remain a hallmark of this blood-soaked conflict."
And for people detained by government forces especially, torture and sexual abuse appear to be the norm.
"It is extremely rare to find an individual who has been detained by the government who has not suffered severe torture," it said.
The commission voiced particular concern over the growing number of attacks on hospitals and medical workers over the past six months, pointing to the dire impact on access to desperately-needed medical care in many places.
"The majority of the attacks have been carried out by pro-government forces," it said.
The investigators also called for an end to the numerous sieges around the country, which have trapped nearly 600 000 people in often-horrific conditions.
And they voiced deep concern over the fate of "at least 300 000 civilians" in rebel-held eastern Aleppo, which was once again completely encircled by government troops on Monday.
The commission also said it was investigating allegations that chemical weapons had been used in the city, saying it had received "reliable information on the use of chlorine gas" on April 5, during the bombing of the Sheikh Maqsoud neighbourhood.
Four people, including two civilians, had been taken to hospital with symptoms of chlorine gas inhalation, it said.
A separate UN investigative panel concluded last month that President Bashar Assad's forces had carried out at least two chemical attacks, one in 2014 and one in 2015.
It also found that Islamic State jihadists had used mustard gas to attack Marea town in northern Aleppo province in August 2015.