UNITED NATIONS — Russia vetoed a British-sponsored draft resolution in the United Nations Security Council on Wednesday condemning the Srebrenica massacre of 1995 as a “crime of genocide,” marking a new low in relations among world powers.

The Russian ambassador, Vitaly I. Churkin, called the language of the measure “confrontational” and “politically motivated,” and urged the Council not to call it to a vote. Saturday is the 20th anniversary of the beginning of a three-day slaughter of about 8,000 Muslim men and boys by Bosnian Serb troops in the Bosnian town of Srebrenica.

The resolution would “doom this region to tension,” Mr. Churkin warned. Russia shares close political ties with Serbia.

Peter Wilson, the British envoy, accused Russia of denying facts established by a special international tribunal. “It is denial, and not this draft resolution, that will cause division,” Mr. Wilson said. “Denial is the final insult to the victims.”