A UN investigative commission has said it believes government forces deliberately bombed a school complex in the country's northern countryside in October, killing 21 children, in a scathing report on crimes committed over the last seven months of the Syrian war.
The UN's Independent International Commission of Inquiry on Syria said government forces and their allies had shown a "complete disregard for civilian life and international law" through continued use of cluster munitions, incendiary weapons and chlorine gas as weapons of war.
It also accused an al Qaida-aligned insurgent group fighting on the side of Syria's rebels and a US-backed Kurdish group for conscripting adolescents for combat.
The commission said the October 26 attack on the Haas village school complex in the rebel-held province of Idlib constituted a war crime.
It said the Syrian air force is the only one known to operate the jets identified in the attack, which was widely reported at the time.
The UN commission's findings came the same day that a Physicians for Human Rights report accused the Syrian government of wilfully denying international shipments of food and medicine to millions of Syrians in besieged areas.
The UN Syria commission's report also concluded that government forces deliberately targeted the capital's water supply infrastructure last December, threatening water supplies to 5.5 million people.
It said the attack was unjustified, and constituted a war crime.
It did not find any evidence that rebels had poisoned the water supply, as state media alleged.
The Syrian government and its ally Russia maintain they are fighting terrorism.
A government delegation led by Syria's UN ambassador Bashar Jaafari, meanwhile, began meetings on Tuesday with Russian officials in the Kazakhstan capital of Astana.
It is the third summit in Astana running parallel to political talks in Geneva between the government and the opposition.
The Astana summits are centred around ceasefire and humanitarian relief co-ordination, but they have borne few results.
Syrian rebels have boycotted this third round, citing the government's continued bombardment of opposition-held areas in Homs and Damascus.
On Monday, activists and the government announced a deal had been reached to evacuate rebels and their families from the Homs neighbourhood of al-Waer, ending more than three years of government siege against the neighbourhood.
Hundreds, if not thousands, of civilians were expected to evacuate al-Waer as well, rather than risk conscription or arrest by the Syrian army and security services.
They will be sent to rebel-held Idlib and other opposition pockets around the country.
The UN condemned a similar agreement that returned the city of Aleppo to government control as a war crime.