Human rights campaigners have warned that Syrian opposition fighters are conducting summary killings, using child soldiers, sectarian violence and committing war crimes, as well as their pro-government foes, cautioning governments about arming the rebel groups.
The Amnesty International report, released this month on the second anniversary of the conflict, comes as David Cameron hinted for the first time that Britain could be prepared to go it alone to supply arms to Syria's rebels, defying a European arms embargo.
He, and the Foreign Secretary William Hague, have stressed the need to identify less-radical groups to combat the worrying rise of Islamic fundamentalism in Syria.
Anti-Syrian regime protesters raise their hands and holding Syrian revolution flags in Aleppo
Ian Lucas MP, Labour’s Shadow Foreign Office Minister, told HuffPost UK: “This report from Amnesty gives a worrying account of the escalating violence in Syria. The appalling human rights abuses which continue to take place must be condemned, particularly the deliberate bombing of civilians.
“Whilst primary responsibility for this conflict rests with President Assad’s forces, Amnesty’s report underlines the need for all sides to now halt the violence and take part in UN-led talks to agree a peaceful political process of transition.”
Shadow Foreign Secretary Douglas Alexander has warned that failures of the international community to stop the conflict were not linked to supplying the rebels with arms.
He wrote in the Guardian on Thursday: "The pressing task remains not to arm the rebels but to unify them.
"The country today is awash with arms and it is impossible to guarantee the end use of weapons given the lack of clarity about the identity, intent and tactics of some of the rebel forces."
In the report, Amnesty warned that armed opposition groups in the country are increasingly resorting to hostage taking, and to the torture and summary killing of soldiers, pro-government militias and civilians they’ve captured or abducted.
It said: "The dead bodies found every day in towns and villages across Syria bearing marks of execution-style killing and torture are the grim evidence of mounting war crimes and other abuses being committed not just by government forces, but also by armed opposition groups."
It warned that any state considering supplying arms must have "a robust monitoring process" and "strong mitigation measures... to allow for any arms transfer subsequently approved to be rapidly halted should evidence emerge that the arms are being or will be used to carry out serious human rights abuses, or are being transferred or diverted to third parties."
Amnesty called on governments to ban the supply of cluster bombs or land mines, which pro-government forces are suspected of using to kill civilians.
It also asked for the United Nations to "refer, as a matter of urgency, the situation in Syria to the Prosecutor of the International Criminal Court for investigation of crimes under international law."
The human rights charity said opposition forces are dumping bodies in a ‘hole of death’ in Damascus, and that children have been used militarily by opposition groups - albeit usually in support roles.
FSA fighters pray after an attack on a Military Academy in Tal Sheer village, north of Aleppo province
Amnesty International Middle East and North Africa Deputy Director Ann Harrison said: “While the vast majority of war crimes and other gross violations continue to be committed by government forces, our research also points to an escalation in abuses by armed opposition groups.
"If left unaddressed such practices risk becoming more and more entrenched - it is imperative that all those concerned know they will be held accountable for their actions.
“Children in Syria are being killed and maimed in increasingly large numbers in bombardments carried out by government forces. Many have seen their parents, siblings and neighbours blown to pieces in front of them. They are growing up exposed to unimaginable horrors.
"With every passing hour of indecision by the international community, the death toll rises. How many more civilians must die before the UN Security Council refers the situation to the prosecutor of the International Criminal Court so that there can be accountability for these horrendous crimes?”
Opposition force abuses recorded in Amnesty’s briefing includes an "execution video" showing a boy - apparently aged between 12 and 14 - holding a machete standing over a man, later identified as Colonel ‘Izz al-Din Badr’.
He lies prostrate on the ground with his hands behind his back. A voice in the background shouts: “He doesn’t have the strength.” The boy brings the machete down on the man’s neck, cheered on by members of an armed opposition group.
Meanwhile, in an area in southern Damascus, witnesses have described a “hole of death” - where armed opposition forces are believed to have dumped the executed bodies of pro-government fighters or those suspected of being informers.
In another case, an Amnesty researcher was told how the body of a man accused of being a collaborator was found after he was killed by an opposition group.
A neighbour told Amnesty: “We immediately went there and found him on a heap of waste, with a bullet hole in the middle of his forehead, a firearm injury to the shoulder … His knee was broken … A brown card hung on him with the words ‘collaborator (awayni), Colonel Helal Eid’.”
An young boy shoots his weapon towards the Syrian Army - Amnesty International have raised concerns over military use of young children in the conflict, even in assistance roles
Civilians have reportedly been killed or injured as a result of armed opposition groups preparing and storing munitions and explosives in residential buildings. The charity also expressed concerns about sectarian violence, and suggested minorities like Shi'a Muslims, Alawite Muslims and Christians were being targeted as they are seen as "pro-government."
The report added: "Opposition fighters or activists closely associated with them or their supporters have attempted to justify such killings to Amnesty International either by claims that every person killed summarily was themselves guilty of killings or by making derogatory statements about these minorities’ support for the government or by acknowledging what they said were ‘mistakes’ or ‘abuses’ committed by the opposition.
"However, no such reasons can be accepted for such killings which are gross human rights abuses and, when carried out by parties to an armed conflict, are war crimes."
Colonel Fou’ad Abd al-Rahman and Colonel Izz al-Din Badr, for example, were abducted by an armed opposition group on 16 August 2012 in Deir al-Zour where they were involved in a military course required for students at al-Furat University.
Both families interviewed by Amnesty International separately said that the abductors introduced themselves as members of an armed opposition group called the ‘Osoud al-Tawhid Battalion’.
They called both families between one to three days after the abduction and asked for a ransom. Colonel Abd al-Rahman’s family said that they had been allowed to speak to him at least once, and that he said he was being tortured and urged them to secure the ransom his abductors had asked for.
At one point, the main abductor negotiating with the two families told Colonel Badr’s wife that he was no longer holding her husband.
She told Amnesty International: "I told the abductor that my husband did not go to Deir al-Zour to fight, he’s just like an employee doing his job at the university… He said, ‘if [the religious committees] find that your husband had committed a wrongdoing, then he shall be killed. If not, then there shouldn’t be a problem’."
The negotiations continued sporadically with both families. Then one of the abductors told Colonel Badr’s wife that she should not keep working on her husband’s case because he and Colonel Abd al-Rahman had been killed and buried in al-Hamidiyeh Garden in Deir al-Zour. A few days later, video footage of the killing of both captive officers emerged.
Colonel Fou’ad Abd al-Rahman’s widow described that terrible moment: “It was around 11am. My daughter [aged 21] shouted to me, ‘mum, come and see dad… quick.’
"He was on TV… as he was shown being killed, I pushed my daughter away to block her from viewing the scene… but she did see. She had a nervous breakdown… she’s become so volatile, she’s traumatised… it’s no easy to see her father in that way… We now want his body back, and we want those who did this to be held accountable.”