Syrian residents stand around a mass grave in the town of Taftnaz, on April 5, 2012
UN investigators said Tuesday said they had "reasonable grounds" to believe both sides in Syria have used chemical weapons, and warned that crimes against humanity were now occurring daily in the war-torn country.
"Allegations have been received concerning the use of chemical weapons by both parties," the Commission of Inquiry on Syria said in a report to the UN Human Rights Council, adding that "the majority concern their use by government forces".
There are "reasonable grounds to believe that chemical agents have been used as weapons," the investigators said.
It was the first time the commission, which has been tasked with probing rights violations in Syria since shortly after the conflict erupted in March 2011, added the suspected use of chemical agents to its long list of war crimes committed in the country.
Without providing details, the report lists four chemical attacks: on the Khan al-Asal neighbourhood of the northern battleground of Aleppo and Uteibah, near Damascus, both on March 19, on the Sheikh Maqsood district of Aleppo on April 13, and on the northwestern town of Saraqab on April 29.
"It has not been possible, on the evidence available, to determine the precise chemical agents used, their delivery systems or the perpetrator," said the report, which covers the period from January 15 to May 15 this year.
"The commission will continue to investigate the allegations of the use of chemical weapons in the conflict, including some occurring more recently than the incidents named," Brazilian commission head Paulo Sergio Pinheiro told the council in Geneva.
A number of diplomats voiced alarm at the suspected use of chemical agents, with the EU representative saying: "Any such use would represent a grave violation of international law."
Commission member Carla del Ponte, a high-profile former war crimes prosecutor, warned however that focusing too heavily on chemical weapons could overshadow the overall suffering in a country where more than 94,000 people have been killed since the conflict began.
The report said "war crimes and crimes against humanity have become a daily reality in Syria," while Pinheiro said: "Syria is in free-fall."
During the four months covered by the report, investigators said 17 suspected massacres took place, out of a total of 30 since the conflict began.
Damascus has so far barred the commission from the country, and investigators have instead based their conclusions on more than 1,600 interviews with refugees and exiles, as well as by Skype and telephone with victims and witnesses inside Syria.
The commission insisted it should be allowed in and also called for Damascus to grant full access for another group of experts tasked by UN chief Ban Ki-moon with investigating chemical weapons allegations, but which has been barred by the regime.
Russia's representative echoed Syrian claims that the report was biased, insisting Damascus had invited the chemical weapons inspectors to probe the Khan al-Asal attack, believed to have been carried out by rebels.
In his speech to the council, Pinheiro said some opposition groups were using child soldiers, which, he said, constitutes "a war crime that causes unspeakable harm to children and destroys families and entire communities."
"We'd like to see all armed groups make a public declaration that children ... under 18 are not welcome in their ranks," he said.
According to the report, 86 child combatants have been killed in the conflict -- nearly half of them in 2013.
The commission and many countries reiterated their call for the deadlocked UN Security Council to refer the situation in Syria to the International Criminal Court in The Hague.
Perpetrators "should know that the world is watching and they will be identified and held responsible," said US representative Eileen Chamberlain Donahoe.
The investigators also called on the international community to refrain from shipping arms to Syria.
Tuesday's report accuses the Syrian army and its allies, including foreign fighters like Lebanese Hezbollah, of suspected "atrocities against women and children," murders, torture, and forced displacements, among other crimes.
It also accuses armed opposition groups of a litany of war crimes, including summary executions and torture, but said they had not reached the scale or intensity of those committed by the regime.