The UN Secretary General Ban Ki-moon and the US secretary of state have urged the international community to speak with one voice on Syria.
Hillary Clinton said that Syria's "horrific campaign of violence" had "shocked the conscience of the world".
Women and children are among those reported to have been tortured and killed on Sunday night in the neighbourhood of Karm el-Zeytoun.
The Syrian government acknowledged the deaths, but blamed "armed terrorists".
Clinton told the UN Security Council meeting in New York that now is the time for all nations - even those who have previously blocked efforts - to stand behind the humanitarian and political approach spelled out by the Arab League.
In a clear reference to China and Russia, she appealed to the international community to "say with one voice - without hesitation or caveat - that the killing of innocent Syrians must stop and a political transition must begin".
Her words echoed those of British Foreign Secretary William Hague, and of Ban who said the Syrian government had "failed to fulfil its responsibility to protect its own people and instead has subjected its citizens in several cities to military assault and disproportionate use of force".
UK Foreign Secretary William Hague said 'The UN has failed on Syria'.