The UN Security Council's inability to pass a resolution on Syria has encouraged the government to step up its assault on the opposition and launch an "indiscriminate attack" on civilians in the city of Homs, the UN human rights chief has said.
Navi Pillay, the UN High Commissioner for Human Rights, said President Bashar al-Assad’s violent crackdown on dissidents indicated crimes against humanity had taken place since March 2011 and were continuing.
"The failure of the Security Council to agree on firm collective action appears to have emboldened the Syrian government to launch an all-out assault in an effort to crush dissent with overwhelming force," Pillay told the UN General Assembly on Monday.
Russia and China vetoed a second UN Security Council resolution on Syria on February 4, the same day a military assault on the central city of Homs began.
Pillay expressed serious concern that the deliberate stirring of sectarian tensions could plunge Syria into civil war and appealed for Assad's government to be referred to the International Criminal Court.
Pillay also said that "credible reports indicate that Syrian security forces killed well above 5,400 people last year, including civilians as well as military personnel who refused to shoot civilians".
Bashar al-Jaafari, Syria's permanent representative to the UN, said Pillay's comments were unprincipled and insisted Syria was coming under attack by terrorist organisations.
Addressing the General Assembly, Jaafari said: "After today how can we trust the High Commissioner for Human Rights on issues related to defending and promoting human rights?"
He called on "all those who host, support, fund, indeed arm terrorist groups to cease forthwith in accordance with the resolutions of international legitimacy".
The government in Damascus blames "armed terrorists" for the unrest in Syria that began after protests calling for freedom erupted across the country more than 11 months ago.
The General Assembly is expected to consider a non-binding resolution similar to the Security Council resolution that Russia and China blocked, backing an Arab League plan that calls for Assad to hand power to his vice president and allow creation of a unity government to clear the way for elections.
Hours after the developments in the UN headquarters in New York, activists said that Syrian troops resumed their bombardment of districts in Homs, making Tuesday the 10th day of shelling and sniper fire on the city.
Activists say that more than 500 people have been killed since the military assault on the city began.
Speaking from Homs, activist Mohammad al-Homsi said the situation was getting worse.
"Army roadblocks are increasing around opposition districts; there is a pattern to the bombardment now. It is heavy in the morning, then gives way to an afternoon lull and resumes at night," Homsi said.
In-depth coverage of escalating violence across Syria
"Shells are falling at random, almost everyone in a residential building in Bab Amr has moved to the ground floor."
Homs' neighbourhood of Baba Amr is an opposition stronghold that activists say has endured shells, mortar attacks and machine-guns by government forces.
Shelling was also reported in the town of Rastan early on Tuesday. Reports of action on the ground are difficult to verify because Syria restricts access by journalists.
That military campaign on Homs prompted the Arab League to ask the United Nations for a joint Arab-UN peacekeeping mission to Syria.
Russia, Assad's close ally and main arms supplier, said on Monday it could not support a peacekeeping mission unless both sides stopped the violence first.
China backed what it termed the Arab League's "mediation" but offered no clear sign of support for the call for a joint peacekeeping force.
"Relevant moves by the United Nations should be conducive towards lessening tension in Syria ... rather than complicating things," said Liu Weimin, a Chinese foreign ministry spokesman.
France also expressed scepticism over any possible deployment of peacekeepers, with Alain Juppe, the foreign minister, saying: "We think that any external military intervention would only make the situation worse."
William Hague, the British foreign secretary, said any peacekeepers should come from non-Western nations.