Hours after a horrific massacre in Homs, China and Russia vetoed a United Nations Security Council resolution on Syria, one which was already watered down in an attempt to get the support of the Russians.

The two permanent council members rejected the draft resolution, which came hours after activists accused Syrian security forces of killing at least 55 people at Homs.

The US ambassador said the vetoes were “shameful”, Britain was “appalled”.

China and Russia defended their move, saying the draft was “unbalanced”.

Earlier, Russian Foreign Minister Sergei Lavrov criticised the draft resolution for singling out the government of President Bashar al-Assad, and not containing measures against armed opposition groups.

But proposed Russian amendments to the text were described as “unacceptable” by the US ambassador to the UN, Susan Rice.

The claim of 55 dead in Homs is pretty conservative. CNN reports that at least 260 were killed in Homs, marking a sadly appropriate 30th anniversary of a Syrian massacre at Hama, carried out when Bashar al-Assad’s father Hafez ruled the country. This included the bombing of residential buildings. The opposition Syrian National Council called it “one of the most horrific massacres since the beginning of the uprising in Syria” in a morning statement.

The fact that Russia still supplies arms to the Syrian security forces clearly weighed heavily on the vote today.

President Obama released a statement saying that Assad had lost his legitimacy and that the Syrian government stands guilty of murder. “Assad must halt his campaign of killing and crimes against his own people now. He must step aside and allow a democratic transition to proceed immediately,” Obama wrote.

Syrian embassies have been attacked by protesters in London, Berlin, Athens and Cairo. And Tunisia severed all diplomatic ties with Syria.

But the Assad government, already isolated before the uprising, hasn’t yet responded to international pressure so far over the past 10 months. And without a new Security Council resolution, there’s less of a chance of a unified front against the repression. Military intervention seems like a remote possibility, especially without UN sanction. The Arab League monitoring process was ineffectual. It’s hard to find much hope for the courageous protesters and the band of military defectors unless those defection rates rise.