Growing numbers of victims of the conflict in Syria are being targeted on account of their religion while gross violations of human rights are occurring on a regular basis, UN investigators said Wednesday.
The new report from a commission of inquiry (CoI) said that violence has been escalating in Syria since May despite the Assad regime's agreement to implement a peace plan the previous month.
The commission, which delivered its report to the UN Human Rights Council in Geneva, also said that it believed many of the victims of a massacre in the central town of Houla last month were killed by pro-government forces.
The findings of the report triggered a walkout by the Syrian delegation after it was read out at the rights council's headquarters in Geneva.
"We will not participate in this flagrantly political meeting," said Syrian ambassador Faisal Khabbaz Hamoui before leaving the hall.
The diplomat denounced a "war of disinformation against Syria" and condemned "criminals" operating there who he said were supported and financed from abroad.
The walkout came as the commission told the council that the unrest was taking on an increasingly sectarian basis.
"Where previously victims were targeted on the basis of their being pro or anti-government, the CoI has recorded a growing number of incidents where victims appear to have been targeted because of their religious affiliation," said the report.
After President Bashar al-Assad told his cabinet on Tuesday that Syria was in a "real situation of war", the CoI agreed that the 16-month revolt against his rule now bore the hallmarks of an armed conflict.
"Gross violations of human rights are occurring regularly, in the context of increasingly militarised fighting which -- in some areas -- bears the characteristics of a non-international armed conflict," said the report.
At the request of the rights council, the CoI focused on the massacre in Houla where at least 108 people were killed in a 24-hour period on May 25-26.
The commission said it was unable to identify the perpetrators but said it suspected forces loyal to Assad of many of the deaths.
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It did not rule out the involvement of anti-government forces seeking to escalate the conflict and punishing non-supporters of the rebellion and also "foreign groups with unknown affiliation".
"The CoI is unable to determine the identity of the perpetrators at this time, nevertheless the CoI considers that forces loyal to the government may have been responsible for many of the deaths."
Syria says the victims, many of them women and children shot in their homes, were killed by 600-800 "terrorists" who flooded in from surrounding villages.
The panel has not been allowed to travel around Syria or access sites such as Houla, basing its findings on interviews, photos and videos.
The commission chair Paulo Pinheiro did however hold interviews in Damascus from June 23-25 with Syria's deputy foreign and deputy justice ministers.
The panel was established last September by the UN Human Rights Council and its latest findings cover the period from February up to June 15.
Government forces have stepped up military operations against areas presumed to be anti-government strongholds, it said in the update.
"Helicopter gunships and artillery have been used in the shelling of entire neighbourhoods believed to be anti-government, even during the presence of observers, as occured in Deir Ezzor and Aleppo in May," it said.
"Homs neighbourhoods of Khaldieh, Al-Qusour, Bab S'baa and the city of Al-Qusayr have effectively become battlefields between the (FSA) Free Syrian Army and government forces."
Anti-government groups are meanwhile employing home-made bombs in assassinations targeting authorities, the army and security forces.
The commission noted the large number of children being killed by snipers and also multiple reports of rape and sexual assault after government forces entered the Baba Amr neighbourhood of Homs in February.
"The fear of rape and sexual assault has restricted the freedom of movement of women and young girls," the report said.
Peace envoy Kofi Annan has called an international meeting on Syria in Geneva on Saturday.