Syria committed crimes against humanity in its crackdown on anti-regime protesters, according to UN investigators in a report published on Monday.

So far the international community has shied away from strong intervention in the region - China and Russia vetoed a UN Security Council resolution placing an arms embargo against Syria in October. Significantly, the region’s powerful states in the form of the Arab League approved sanctions against Syria on Sunday.

For international criminal law to play a role in the unfolding story, yesterday’s UN investigation needs to lead to International Criminal Court arrest warrants being issued for President Assad and other senior figures in the regime. For that to happen the UN Security Council must ask the ICC to investigate (as it did recently in the case of Libya); or the ICC Prosecutor must take the initiative to investigate, as he did last year in Kenya.

State forces have murdered, raped and tortured demonstrators since the beginning of protests in March this year, according to evidence gathered by the Independent Commission of Inquiry on Syria.

The panel interviewed 223 victims and witnesses, among them security force defectors, who told of shoot to kill orders to crush demonstrators and cases of children being tortured to death.

"The commission is gravely concerned that crimes against humanity have been committed in different locations in the Syrian Arab Republic during the period under review," it said in its report, while concluding that military and security forces were behind the acts.

"The sheer scale and consistent pattern of attacks by military and security forces on civilians and civilian neighbourhoods and the widespread destruction of property could only be possible with the approval or complicity of the State," the panel said.

Defectors from military and security forces told the commission that they received orders to shoot at unarmed protesters without warning.

They, together with militias, had conducted joint operations with "shoot to kill" orders, notably in Al Ladhiqiyah in early April and in a suburb of the city in August.

"The protesters called for freedom. They carried olive branches and marched with their children," a witness was quoted as saying.

"We were ordered to either disperse the crowd or eliminate everybody, including children. We opened fire."

The panel heard of sniper attacks on people leading marches and on those trying to rescue the wounded.

Torture and killings reportedly took place in the Homs Military Hospital by security forces dressed as doctors and abuse of detainees was described as "rampant" at the detention facilities of the Air Force Intelligence Branch at Mazzeh airport near Damascus.

The report highlighted the case of 14-year-old detainee Thamir Al Sharee from the town of Sayda whose postmortem showed injuries consistent with torture.

A 40-year-old man told the panel he witnessed the rape of an 11-year-old boy by three security services officers.

The commission said Syria had violated the right to life, to peaceful assembly and to freedom of movement among others.

It called on the government to put an "immediate end to gross human rights violations" and launch an independent investigation into the violence.

The report also acknowledged the existence of the "Free Syrian Army," a group of defectors it said had claimed responsibility for armed attacks against military and security forces and in its list of recommendations the panel urged opposition groups to respect international human rights law.

The Human Rights Council set up the commission in August to investigate human rights violations in Syria where the UN estimates at least 3,500 people have been killed.

The panel met with regional organisations including the Organization of the Islamic Conference and the Arab League as it gathered evidence from the end of September to the middle of November but was not allowed to carry out its work inside Syria.

The council will study the report by the three experts, Karen Koning AbuZayd from the United States, Turk Yakin Erturk and Paulo Sergio Pinheiro from Brazil, at its 19th session taking place in March.