Syria's top diplomat was summoned to the Foreign Office on Monday as its political director condemned a "sickening" massacre which saw dozens of children killed.
Sir Geoffrey Adams told the Syrian Chargé d’Affaires the UK condemned Friday's massacre in the city of Houla which saw 108 killed, including at least 49 children.
The Foreign Office said in a statement that Sir Geoffry has called for an "urgent internal investigation" in Syria, adding that "those responsible for acts of violence should be identified and held accountable."
Grim: UN observers at a hospital morgue in Houla, where civilians were massacred
"Sir Geoffrey said that unless the Syrian regime ceased all military operations immediately and implemented Kofi Annan’s six point plan in full, the international community would take further quick and robust action in response."
The Syrian government was accused by the United Nations of an "outrageous use of force" against civilians in an attack on Friday that left more than 100 dead, including at least 49 children.
Another 41 people, including five women and eight children, have been killed by Syrian army shelling in the city of Hama in the past 24 hours, according to news agency Reuters.
An amateur video claiming to show an injured child in Houla
Using information from an opposition group, it reported that tanks and soldiers opened fire on civilian neighbourhoods yesterday, in retaliation for rebel attacks on government road blocks.
Russia and China have so far been the principal opponents of stronger action against the Syrian regime by the UN.
China condemned the killings on Monday in Houla but stopped short of putting blame for the massacre of 100 people at the door of President Bashar al-Assad's regime.
Monitors: Members of the UN Supervision Mission in Syria visit the capital Damascus
“The Chinese foreign ministry condemns in the strongest possible terms the cruel killings of ordinary citizens, especially women and children," the government said in a statement.
Russia has repeatedly warned that the international community risks sparking a civil war if it sides too heavily with opposition forces in Syria.
The Foreign Office added in their statement that Sir Geoffrey had "He restated that the responsibility to end the violence lay squarely with Assad and those around him, and that spiralling conflict and worsening sectarian violence was a product of the regime’s brutal response to dissent. "