Rupert Colville, a spokesman for the U.N. High Commissioner for Human Rights, said most of the 108 people killed in Houla last weekend were executed. He added that entire families were apparently shot to death in their homes by Syrian authorities.
Russian Foreign Minister Sergei Lavrov expressed his concern over the weekend's events in Houla. He told former U.N. Secretary-General Kofi Annan that an "objective and unbiased" probe should be carried out under the authority of the U.N. Supervision Mission in Syria, Russia's state-run news agency RIA Novosti reports.
Russia and China, two veto-wielding members of the Security Council, have expressed reservations over formal action against Syria at the United Nations out of fear of further militarization of the conflict. Russia is one of Syria's largest military customers.
White House spokesman Jay Carney said members of the Security Council were considering punitive measures against the Syrian government should it "continue to refuse" to comply with the terms of a peace plan that was acknowledged in April.
While military action was still on the table, he said, further militarization would "lead to greater chaos, greater carnage" in Syria.