Syrian President Bashar al-Assad has held talks with United Nations-Arab League envoy Kofi Annan in Damascus, amid intensifying international concern about the bloodshed in Syria.
The talks on May 29 follow the May 25 killing of at least 108 people, mainly women and children, in the village of Houla.
On May 28, Annan called the massacre "an appalling moment with profound consequences," saying those responsible must be held to account.
He has urged "everyone with a gun" to abide by his six-point peace plan to help end the violence.
The UN Security Council has condemned the Syrian army's use of artillery and tanks at Houla.
Witnesses and opposition fighters have accused Alawite militia loyal to Assad's regime of involvement in the bloodshed.
Damascus has accused opposition fighters of responsibility.
The UN's High Commissioner for Human Rights said on May 29 that most of the victims of the Houla massacre were summarily executed in two separate incidents within the Taldo neighborhood of the town.
Rupert Colville, a spokesman for the UN body, said fewer than 20 of the 108 killings can be attributed to artillery and tank fire. He said most of the rest were executed.
UN monitors said spent tank and artillery shells, as well as fresh tank tracks on the ground, were clear signs of the Syrian government's involvement.
But the UN monitors said they were unable to confirm who used knives and guns at close range against women and children.
'Message Of Peace'
Upon his arrival in Damascus on May 28, Annan indicated that his talks with Assad would be "serious and frank," and that he would call on Assad's regime to "take bold steps" to signal a serious intention to resolve the Syrian crisis peacefully and "help create the right context for a credible political process."
"This message of peace is not only for the government, but for everyone, every individual with a gun," he said. "The six-point plan must be implemented comprehensively and this is not happening today."
Annan's peace plan calls for heavy weapons to be pulled out of towns and cities, followed by an end to fighting, and a political dialogue.
Although Damascus says it withdrew heavy weapons from residential neighborhoods before an April 12 deadline, analysts say the regime's claim is belied by the shelling of Houla, Hama and other Sunni-dominated areas,
Russia and China -- longtime defenders of Assad's regime who have blocked previous moves for UN action -- on Sunday backed a non-binding UN Security Council statement that criticized the Syrian army's use of artillery and tanks at Houla.
In the aftermath of the massacre, China and Russia have both urged a renewed push for the implementation of Annan's peace plan.
China said it was "deeply shocked by the large number of civilian casualties in Houla, and condemns in the strongest terms the cruel killings of ordinary citizens, especially women and children."
Moscow has grown increasingly critical of Damascus in recent months, and Russian Foreign Minister Sergei Lavrov's latest comments were seen as being unusually strong.
Although he says opposition forces have "terrorists" among them, on May 28 Lavrov put the blame for the past 15 months of carnage in Syria primarily on Assad's government.
Iran has remained solid in its support for Assad's regime. Tehran has also denied reports that it has been helping Syrian forces crack down on anti-regime protesters.