Prime Minister David Cameron today condemned killing of 100 people including many women and children by Syrian government forces, describing the attack as “brutal and sickening” and called for “concerted action” from the international community.

The British-based Syrian Observatory for Human Rights (SOHR) reported that the massacre was carried out at a farm by pro-regime militiamen armed with guns and knives after regular troops had shelled the area.

Activists have blamed government-linked militia groups for killing of dozens of people in the villages of Qubair and Maarzaf. During a visit to Norway, Cameron said the massacre was further proof that the Assad regime was “completely illegitimate and cannot stand”.

Referring to Russia and China, countries which have blocked international action against Assad, the Prime Minister said the whole world should show that it wants a transition to a new regime in Damascus.

Meanwhile, today Syria envoy Kofi Annan will appear before the United Nations General Assembly and Security Council. The US, the UK, France and others have repeatedly warned that Syria risks plunging into a civil war if the situation remains same.

But despite these concerns, Annan’s plan remains the only realistic hope. UK ambassador to the UN Sir Mark Lyall Grant said, “The Annan plan is on life support, but it is not dead.”

The core of Annan’s proposal, would be the establishment of a contact group that would bring together Russia, China, the United States, Britain, France and key regional players with influence on Syria’s government and the opposition, such as Saudi Arabia, Qatar, Turkey and Iran.

If such a group is created, envoys said, Annan would be trying to break the deadlock among the five permanent council members that has pitted veto powers Russia and China against the US, Britain and France and prevented any meaningful UN action on the Syrian conflict.