A senior State Department official warned Russia on Wednesday against deploying nuclear weapons in Crimea, and said the United States and its allies would respond if Moscow opted to do so.Victoria Nuland, assistant secretary of state for European and Eurasian affairs, said such a move by Russia would be "extremely dangerous," the Washington Free Beacon reported.Nuland, speaking at the American Enterprise Institute, did not explain what form the U.S. response might take. Russian Foreign Minister Sergei Lavrov said Monday that "Russia has every reason to dispose of its nuclear arsenal" on the Crimean Peninsula, which it annexed in March.In late February and early March, heavily armed pro-Moscow separatists occupied Crimea, which had been part of Ukraine since the 1950s. In mid-March, the separatists staged a referendum in which almost 97 percent of Crimea's residents purportedly voted to become part of Russia. Many international observers have condemned the vote as illegitimate."Crimea belongs to Ukraine," Nuland said. "Any effort to further militarize that region will be extremely dangerous and will not be unanswered by those of us who also live in that neighborhood."Nuland said providing lethal assistance to the Ukrainian military remains "under review" by the Obama administration. The most important thing, she said, is to ensure that Russia is "deterred" from further hostile actions in Ukraine.Nuland said that since early September – when pro-Russian separatists and the Ukrainian government signed what was supposed to have been a ceasefire agreement – Moscow has illicitly transferred close to 500 pieces of military equipment to the rebels. United Nations officials said earlier this week that more than 1,300 people – an average of 13 a day – have been killed in eastern Ukraine since the ceasefire agreement was reached.