The UN-Arab League Envoy to Syria Kofi Annan has met President Bashar al-Assad to discuss the mass killing of civilians on Friday.
The former UN secretary general left the presidential palace after a meeting of around two hours. He had been expected to urge compliance with his six-point plan designed to restore peace to the country.
The attack on the town of Houla, near the restive city of Homs, resulted in the deaths of more than 100 people including at least 49 children. Images of the attack have shocked the world and provoked condemnation from many countries including Syria's allies Russia and China.
Soon after arriving in Damascus on Monday, Mr Annan told reporters that his Six-Point Plan for peace was not being implemented and he called on "every individual with a gun" to do so.
On Sunday, members of the UN Security Council accused the Syrian government of an "outrageous use of force" against civilians.
– UN Security Council Statement
The Security Council condemned in the strongest possible terms the killings, confirmed by United Nations observers, of dozens of men, women and children and the wounding of hundreds more in the village of (Houla), near Homs, in attacks that involved a series of government artillery and tank shellings on a residential neighbourhood.
The Security Council also condemned the killing of civilians by shooting at close range and by severe physical abuse.
Such outrageous use of force against civilian population constitutes a violation of applicable international law and of the commitments of the Syrian Government under United Nations Security Council Resolutions.
China has also condemned the "cruel killing" of civilians today and called on "all sides concerned" to implement the Annan plan "immediately, comprehensively and thoroughly".
Kofi Annan will hold talks with the Syrian Foreign Minister in Damascus today about the attack. He is due to meet President Bashar Assad on Tuesday.
President Assad's regime has denied it is behind the slaughter and condemned the "tsunami of lies" blaming it for the massacre.
The Foreign Secretary William Hague has been discussing the attack in Syria with his Russian counterpart Sergei Lavrov in Moscow.
In a joint press conference, Mr Hague said he believes the Syrian government has "primary" but not sole responsibility for the violence, but that Kofi Annan's peace plan was "at the moment the only hope".
Russia's Foreign Minister was more circumspect saying: "We are dealing with a situation in which both sides evidently had a hand in the deaths of innocent people".
Earlier, Mr Hague said he was "absolutely sickened" by the onslaught on civilians and said he would summon the Syrian Charge d'affaires in London to the Foreign Office.
He dismissed the claims of President Assad's regime that it was not responsible and he called for international action to prevent Syria descending into a full civil war.
The Syrian Government has been denying claims that its forces were responsible and said that an investigation is underway.
Foreign ministry spokesman Jihad Makdissi said that Syria is being subjected to:
A tsunami of lies... We categorically deny the responsibility of government forces for the massacre.
Speaking to ITV News one Syrian resident described what he saw in Houla:
– ABO EMAD, SYRIAN RESIDENT, IN HOULA YESTERDAY
Yesterday when I arrived to Al Houla all I saw is the crying people.
The people who lost their children, lost their parents. Until yesterday we had 106 people killed in one night in Al Houla only. I cannot tell you the funerals where going on.
The UN monitors refused to come at first to stop the massacres. They said they are not allowed to go at night. The shelling continued for second day today. There are still a lot of bodies - we are finding them today.
The monitors came today and looking with us for the dead bodies. We're asking the international community to do something about this.
With the final countdown underway to the London Olympics, the Deputy Prime Minister Nick Clegg suggested Syrian representatives could be banned from coming if their human rights record is in doubt.
Pictures from The Andrew Marr Show, BBC1