The UN human rights chief has asked the Security Council to refer Syria to the International Criminal Court for the investigation of alleged atrocities against anti-government protesters.
Navi Pillay's remarks on Thursday came hours after the US President Barack Obama and the European Union explicityl called on Syrian President Bashar al-Assad to step down.
Navi Pillay told reporters after the Council meeting in New York City that she recommended the referral because a UN fact-finding commission reported that its evidence supported a finding of "widespread and systematic violations'' of human rights and crimes against humanity.
However, she said she did not "hold out much hope'' for a court referral.
After the meeting, Syria's UN Ambassador Bashar Ja'afari said the United States is waging a "diplomatic and humanitarian war" against Syria, along with some other UN Security Council members.
"All the wars and invasions that were taken on behalf of this Security Council were based on lies." Ja'afari told reporters.
"The Iraqi weapons of mass destruction opened the way for the Security Council to invade Iraq. It was a big lie, acknowledged by [former US Secretary of State] Colin Powell as we all know.
"So nothing happens but lies when it is related to the activities of these influential members of the Security Council who are using the Security Council as an instrument to justify their illegitimate actions."
But Syria will now apparently allow the United Nations to visit the country, which it did not permit Pillay's investigators to do.
Valerie Amos, chief of the Office for the Co-ordination of Humanitarian Affairs, said on Thursday that a mission from her office will visit over the weekend.
Earlier on Thursday, Obama issued a written statement saying: "The future of Syria must be determined by its people, but President Bashar al-Assad is standing in their way ... For the sake of the Syrian people, the time has come for President Assad to step aside."
Obama said the US "cannot and will not impose this transition upon Syria" but will support "an effort to bring about a Syria that is democratic, just, and inclusive for all Syrians. We will support this outcome by pressuring President Assad to get out of the way of this transition".
Obama said Syrians "have spoken with their peaceful marches" and that the Syrian government "has responded with a sustained onslaught".
In-depth coverage of escalating violence across Syria
"I strongly condemn this brutality, including the disgraceful attacks on Syrian civilians in cities like Hama and Deir ez-Zor, and the arrests of opposition figures who have been denied justice and subjected to torture at the hands of the regime," the president's statement said.
Obama also announced a new round on US sanctions to target Syria's energy sector, banning US imports of Syrian petroleum and petroleum products and prohibiting Americans from dealing in such products.
Syria is not a main source of oil for the US, but if European allies join the effort, it could significantly affect
one of the Syrian government's top sources of revenue.
Syrian crude oil exports go mostly to European countries such as Germany, Italy, and France, according to the US Energy Information Agency.
Shortly after Obama issued his statement, the European Union also called for Assad to step down and warned of further sanctions.
"The EU notes the complete loss of Bashar al-Assad's legitimacy in the eyes of the Syrian people and the necessity for him to step aside," the EU's foreign policy chief, Catherine Ashton, said in a statement.
Fawaz Gerges, a professor of Middle East politics, comments on the mounting international pressure
The UN fact-finding commission said in a report released on Thursday that it had compiled evidence implicating 50 people at various levels of government who could be prosecuted over the Syrian crackdown.
The team, which was not allowed into Syria, interviewed victims and witnesses in the region from mid-March to mid-July.
Syrian forces had fired on peaceful protesters throughout the country, often at short range and without warning, killing at least 1,900 civilians up to mid-July, including children, investigators said in the report.
Their wounds were "consistent with an apparent shoot-to-kill policy", it said.
Protesters took to the streets across Syria on Thursday night, including in the eastern city of Deir ez-Zor, Homs and several towns in Deraa governorate in the south.
Activists said the security forces continued its crackdown in several cities despite claims by the Assad government that military and police operations against protesters had stopped.
Shooting was reported in the central city of Homs and in the Damascus suburb of Dumeir.
Rights group Avaaz said there been fresh attacks on civilians in Latakia earlier in the day, with regime forces claiming to crack down on "terrorist gangs" in the Palestinian camp of al-Ramel.
The Local Co-ordination Committees (LCC) said security forces backed by army were carrying out arrests in Deir ez-Zor.
The UK-based Syrian Observatory for Human Rights said soldiers and members of the security forces took up positions in the town of Zabadani outside Damascus and in some of the capital's suburbs.