Syrian government aircraft deliberately bombed and strafed a humanitarian convoy, killing 14 aid workers and halting relief operations, U.N. investigators said on Wednesday in a report identifying war crimes committed by both sides in Syria's war.
Syrian and Russian forces conducted daily air strikes on rebel-held eastern Aleppo between July and its fall on December 22, killing hundreds and destroying hospitals, they said.
Orphanages, schools and homes were "all but obliterated", panel chairman Paulo Pinheiro told a news conference.
Opposition groups shelled government-controlled western Aleppo, killing and injuring dozens, the report said. They prevented civilians from fleeing besieged eastern Aleppo, using them as human shields - a war crime.
"The scale of what happened in Aleppo is unprecedented in the Syrian conflict. Much of Aleppo, once Syria's biggest city and its commercial and culture centre and a UNESCO World Heritage site, has been reduced to rubble," Pinheiro said.
He called for ensuring that "those responsible for this ruinous situation one day are brought to justice".
His team was ready to share its confidential list of suspected war criminals on all sides with a new U.N. body on Syria being set up in Geneva to prepare criminal prosecutions.
"It cannot pass without having this step toward justice, because of the great numbers of victims," panel member Carla del Ponte said.
"What we have seen here in Syria, I never saw that in Rwanda, or in former Yugoslavia, in the Balkans. It is really a big tragedy," she added. "Unfortunately we have no tribunal."
Cluster munitions were "pervasively used" and air-dropped into densely populated areas, the report said, amounting to the war crime of indiscriminate attacks.
"We have established very clearly in the report that the Syrian air force is responsible for these attacks, we don't have any evidence linking Russia to those attacks with forbidden chemical weapons," Pinheiro said.
The investigators also did not attribute any specific war crime investigated to Russian forces but Pinheiro said they would to assign responsibility "if and when we can prove it".
The U.N. Commission of Inquiry's report - released as Syrian peace talks continue in Geneva - covers the July-December period and is based on 291 interviews with victims and witnesses, as well as analysis of forensic evidence and satellite imagery.
Syrian helicopters unleashed toxic chlorine bombs "throughout 2016" on Aleppo, a weapon that caused hundreds of civilian casualties there, it said.
At least 5,000 pro-government forces had encircled eastern Aleppo in a "surrender or starve" tactic. Thousands of civilians had to leave the city under an evacuation agreement between the warring parties that amounted to the war crime of forced displacements, it said.
"This represents - and we have said this in the past - a worrying pattern that has occurred in other areas of the country including Deraa and Moadamiya," Pinheiro said.
The investigators accused the Syrian government of a "meticulously planned and ruthlessly carried out" air strike on a U.N. and Syrian Red Crescent convoy at Orum al-Kubra, in rural western Aleppo on Sept. 19 that killed 14 aid workers.
At the time, the Syrian army and Russia denied responsibility for the attack. A previous U.N. inquiry had been unable to determine who conducted the strike.
"By using air-delivered munitions with the knowledge that humanitarian workers were operating in the location, Syrian forces committed the war crimes of deliberately attacking humanitarian relief personnel, denial of humanitarian aid, and attacking civilians," the report said.