The United States, Britain and Russia have each called for a halt to the violence in Syria, but the United Nations Security Council remains divided on how to resolve the crisis in the country.
Security Council foreign ministers met Monday in New York, following a two-day trip to Syria by former U.N. secretary-general Kofi Annan that ended without a settlement. Annan is scheduled to meet Tuesday in Ankara with members of the Syrian opposition.
U.S. Secretary of State Hillary Clinton called on Russia and China to join international "humanitarian and political efforts" to end the violence, which she blamed directly on Syrian President Bashar al-Assad's "military machine."
"There must be a cessation of violence by the Syrian regime first and foremost," she said. "Then we can move toward asking others - who will no longer need to defend themselves because we will be in a political process - to end their own counter-violence."
Her Russian counterpart, Sergei Lavrov, agreed that Syrian authorities "bear a huge share of responsibility." But he insisted that armed elements of the Syrian opposition also are responsible for the crisis, and that the Security Council must act "without imposing any prejudged solutions."
"Cease-fire is an absolute must and we sincerely hope that the mission headed by Kofi Annan would succeed in developing some ideas which would make it possible for us to agree on how to stop the bloodshed immediately, how to stop the fighting, irrespective of the source of the violence," he said.
Russia and China have vetoed Security Council resolutions condemning the Syrian government's deadly crackdown on its opponents. They say the resolutions call for interfering in Syria's internal affairs.
British Foreign Secretary William Hague said the Security Council has "failed" in its responsibilities to the Syrian people and that the diplomatic challenge now is to build on areas where the international community agrees.
"It is encouraging that everybody is talking about a political process. Everybody is now talking about humanitarian aid being delivered, about a cessation of violence and everybody on the United Nations Security Council of course is supporting the work of Kofi Annan," he said. "So there are now many common elements, but the task of bringing them together in a resolution remains."
On Monday, investigators told the U.N. Human Rights Council in Geneva that Syria's government has subjected civilians to collective punishment and that its forces are accused of carrying out executions and mass arrests in Homs.
U.N. humanitarian chief Valerie Amos visited the city last week, including a stop in the battered district of Baba Amr. She told reporters in New York Monday that she was "horrified by the destruction" she saw there and is worried about the condition of the area's residents.
"I am extremely concerned as to the whereabouts of the people who have been displaced from Baba Amr by the shelling and other violence. I was told that some 50-60 thousand people used to live in the area. We need to know what has happened to them, where they are now, and what they need," she said. "We also need to know where the wounded are, and whether they are receiving treatment."
Her comments came as Syrian activists and the government traded blame for the deaths of dozens of men, women and children in the Homs neighborhood of Karm el-Zeytoun.
Activists said soldiers and pro-government militias were responsible for the killings. State-run media in Damascus confirmed the deaths, but said "armed terrorists" had killed the victims and filmed their bodies in order to influence discussions at the United Nations in favor of "foreign interference" in Syria.
Both sides deny responsibility. Syrian restrictions on independent reporting make it impossible to reconcile the contradictory accounts of the killings.
Amateur videos posted on the Internet show the mutilated corpses of at least 45 victims in the neighborhood where the deaths occurred Sunday. The Syrian Network for Human Rights said the army arrested several families and took them to "shabiha" militias in nearby neighborhoods known for supporting the government. The London-based group said about 30 men were tortured, shot, doused with gasoline and set on fire, and that women and children were killed separately.
Leaders of the Syrian National Council, the main expatriate opposition group, later issued a statement calling for the international imposition of a no-fly zone, safe corridors for civilians, and weapons for the Free Syrian Army.
U.N. officials estimate that 7,500 people have died in the year-long violence.
Some information for this report was provided by AP, AFP and Reuters.