Syria's air force deliberately bombed water sources in December, a war crime that cut off water for 5.5 million people in and around the capital Damascus, the UN Independent International Commission of Inquiry on Syria said on Tuesday.
The commission said it had found no evidence of deliberate contamination of the water supply or demolition by armed groups, as the Syrian government maintained at the time.
Rebels had controlled the springs of the Wadi Barada valley, northwest of Damascus since 2012 and faced a major offensive by Syrian government forces and their allies, despite a ceasefire deal. The rebels withdrew at the end of January.
The commission, led by Brazilian investigator Paulo Pinheiro, said there were no reports of people suffering water contamination on or before December 23, when the Syrian air force hit al-Fija spring with at least two air strikes.
"While the presence of armed group fighters at [the] spring constituted a military target, the extensive damage inflicted to the spring had a devastating impact on more than five million civilians in both government and opposition controlled areas who were deprived of regular access to potable water for over one month," the commission's report said.
"The attack amounts to the war crime of attacking objects indispensable for the survival of the civilian population, and further violated the principle of proportionality in attacks."
The commission's conclusions were based on interviews with residents and satellite imagery, as well as publicly available information.
The report, which covered the period between July 21, 2016, and February 28 this year, came less than two weeks after the commission said that Syrian government aircraft deliberately bombed and strafed a humanitarian convoy, killing 14 aid workers, in September last year.
In a separate incident, aircraft – most likely Syrian or Russian – bombed the longstanding headquarters of the Syrian Arab Red Crescent in the town of Idlib, Tuesday's report said.
The commission also documented the use of lethal chlorine gas on multiple occasions by government and pro-government forces, in the suburbs of Damascus and Idlib province.
There was no evidence of Russian involvement in chlorine attacks, the report said.
(Reporting by Tom Miles; Editing by Dominic Evans)