UN monitors in Syria say the army is preventing them from reaching the village of Qubair, where 78 people are reported to have been massacred.

“They are being stopped at Syrian army checkpoints and in some cases turned back,” mission commander Gen Robert Mood said.

“Civilians” were also stopping UN patrols in the area near the western city of Hama, he added.

US Secretary of State Hillary Clinton said the violence was “unconscionable”.

The UN has 297 unarmed observers in Syria to verify the implementation of a peace plan negotiated by UN-Arab League envoy Kofi Annan, which includes a ceasefire that supposedly came into force in mid-April