Russia has vetoed a UN resolution that would have condemned the 1995 massacre of Muslim men at Srebrenica during the Bosnian war as a "crime of genocide".
It said that singling out the Bosnian Serbs for a war crime would create greater division in the Balkans.
Two international courts have called the slaughter by Bosnian Serbs of some 8,000 Muslim men and boys who had sought refuge at what was supposed to be a UN-protected site genocide.
But Russia's UN ambassador Vitaly Churkin objected to focusing only on Srebrenica, stressing that Bosnian Serbs and Croats had also suffered during the war.
The defeated resolution, drafted by Britain, states that acceptance of "the tragic events at Srebrenica as genocide is a prerequisite for reconciliation" and "condemns denial of this genocide as hindering efforts towards reconciliation".
Mr Churkin and China's UN ambassador Liu Jieyi appealed to the council not to put the resolution to a vote, citing divisions among its 15 members.
But Britain's deputy ambassador Peter Wilson insisted that the vote go ahead. The vote was 10 in favour, Russia casting a veto and four abstentions including China.
Leaders of the Bosnian Serbs and Serbia, who have close religious and cultural ties to Russia, have lobbied President Vladimir Putin to vote No.
Serbian prime minister Aleksandar Vucic said after an emergency meeting of the government last night that the British resolution opened fresh divisions and "pushed us into the trenches of hatred".
Mr Wilson said after the vote that Britain was "outraged" by Russia's veto.
"Russia's actions tarnish the memory of all those who died in the Srebrenica genocide," he said.
"Russia will have to justify its behaviour to the families of over 8,000 people murdered in the worst atrocity in Europe since the Second World War."