Updated 11:45 ET
Russia vetoed a draft U.N. resolution on Saturday that would have declared Crimea's referendum illegal, and its close ally China abstained, heightening the Kremlin's isolation.
Russia has a veto right as one of the five permanent member of the U.N. Security Council, and had signaled it would block the draft resolution, the Associated Press reports.
Samantha Power, U.S. ambassador to the U.N., condemned Russia's move and its "unlawful" incursion into Ukraine. "The Russian Federation has the power to veto a Security Council resolution, but it does not have the power to veto the truth," she said. "Russia cannot change the fact that moving forward in blatant defiance of the international rules of the road will have consequences."
The veto came as a rally in central Moscow against Russia's intervention in Ukraine attracted tens of thousands of protestors, indicating a measure of popular dissent with the tactics of Russian President Vladimir Putin.
Protestors waved Ukrainian and Russian flags and shouted slogans often heard in Kiev during anti-government demonstrations, urging Putin to withdraw his troops from Crimea and stop menacing eastern Ukrainian provinces with large troop formations, Agence France Presse reports. Meanwhile, Ukrainian forces reported that 120 Russian troops seized a natural gas distribution center near Crimea, its first military move outside of the peninsula.
Marchers carried signs reading "Putin, get out of Ukraine" and called an invasion of the country a "fratricidal war," referring to the close cultural bonds between the two Slavic countries.
The large turnout reflected the results of a Kremlin-sponsored poll last month that showed 73 percent of Russians oppose interfering in Kiev. Russian police, who often downplay attendance at protests, said only 3,000 showed up to demonstrate.
Crimea is preparing to hold a referendum Sunday that would lead to its annexation by the Kremlin. Western leaders have called the referendum illegitimate, saying the presence of Russian troops in Crimea has violated Ukrainian sovereignty and caused an atmosphere of intimidation in the peninsula.