UN-Arab League envoy Mr Annan said he was “horrified” by the killings in Houla and urged the Syrian government to take bold steps to show it was serious about reaching a peaceful solution to the crisis, ahead of today’s talks.
The former UN secretary-general called on “every individual with a gun” to lay down their arms and described the negotiations as a “critical moment” in the crisis, which has claimed at least 10,000 lives since protests broke out in March 2011.
The latest diplomatic efforts come as some world leaders hardened their stance, with Russia’s foreign minister, Sergei Lavrov, whose government is a close ally of the Syrian regime, saying he was “deeply alarmed” by the slaughter.
The Chinese government, which has also previously resisted joining western and Arab League sanctions against Mr Assad, condemned the killings.
It said “China feels 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”.
Meanwhile, Syrian diplomats were yesterday summoned to the Foreign Office to hear the UK government’s criticism, with Foreign Secretary William Hague using a visit to Moscow to say he was “absolutely sickened” by the attack on civilians.
Foreign Office political director Sir Geoffrey Adams, who summoned the Syrian chargé d’affaires, described the killings as “a sickening and evil crime”.
Prime Minister David Cameron and French President François Hollande discussed the situation by phone, reaffirming their “full support” for Mr Annan’s six-point peace plan, which envisages a truce leading to dialogue between the government and opposition aimed at a Syrian-led political transition.
Syria has strongly denied allegations that its forces carried out the killings, but the UN Security Council, after an emergency session, condemned government forces for shelling residential areas as it talked about an “outrageous use of force” against civilians.
The security council’s statement said “those responsible for acts of violence must be held accountable,” and asked the UN observer mission and secretary-general Ban Ki-moon to investigate the attacks that violated international law.
Mr Annan said the killing of 108e, including 49 children and 39 women, was “an appalling crime, and the security council has rightly condemned it”.
Mr Annan, said: “I urge the [Syrian] government to take bold steps to signal that it is serious in its intention to resolve this crisis peacefully, and for everyone involved to help create the right context for a credible political process. This message of peace is not only for the government, but for everyone with a gun.”
Mr Annan brokered a ceasefire agreement for 12 April, part of a broader six-point plan aimed at ending the bloodshed and leading towards a negotiated solution. But it has not held and hundreds of people have been killed in the past six weeks.
Mr Annan said: “The six-point plan has to be implemented comprehensively, and this is not happening. I have come to Syria at a critical moment in this crisis, I am personally shocked and horrified by the tragic incident in Houla.”