Russia has been exposed as isolated over the crisis in Ukraine, with members of the UN Security Council overwhelmingly supporting a draft resolution condemning an upcoming referendum on the future of Crimea as illegal.
The vote on Saturday comes as reports claimed that Russian troops had landed on a strip of land in the southeast between Crimea and the mainland, forcing Ukraine to dispatch an aircraft and armed forces to stop the troop movement.
Russia vetoed the US-backed resolution when it was put to a vote before the council, but its ally China abstained, leaving it as the only nation to recognise the Crimean referendum.
The veto means the resolution will not be adopted by the UN, but highlights Russia's international isolation over Crimea.
After the vote was taken, Samantha Power, the US ambassador to the UN, said: "Under the UN charter, the Russian Federation has the power to veto a security council resolution. But it does not have the power to veto the truth."
"History has lessons for all of us, who are willing to listen. Unfortunately, not everyone was willing to listen today."
Al Jazeera's diplomatic editor, James Bays, said the vote laid bare the international opposition to Russia's stance on Ukraine and Crimea.
"China is not supporting its ally Russia on this occasion. It is abstaining. That's the best the Western nations, who drafted this resolution, could hope for, but they think that this is important because it exposes that Russia is on its own."
Before the vote, Russia's ambassador to the UN, Vitaly Churkin, said that Russia's action in Crimea arose because of an "unconstitutional coup" in Kiev.
Meanwhile, Ukraine accused Russia of further incursion into its territory, which the US said would be an "outrageous escalation" if proven to be true.
"For something additional, even more escalatory to have occurred would be flying in the face of everything you have heard here today," Ambassador Power said.
Pro-Russian leaders in Crimea were making final preparations for a referendum widely expected to transfer control of the region to Russia, despite denunciation by Ukraine and threats of Western sanctions.
|Crimea faces uncertain future after referendum
On Saturday, Ukraine's acting president, Oleksander Turchinov, accused "Kremlin agents" of fomenting deadly violence in eastern cities of Donetsk and Kharkiv, ahead of the vote on Sunday.
Ukraine's parliament meanwhile voted overwhelmingly to dissolve Crimea's assembly, while demonstrators staged large protests in Ukraine and in the Russian capital Moscow, for and against the referendum.
Three people died in two incidents on Friday, including two in a reported shootout in the eastern city of Kharkiv.
On the eve of a breakaway vote, Turchinov told politicians: "You know as well as we do who is organising mass protests in eastern Ukraine - it is Kremlin agents who are organising and funding them, who are causing people to be murdered."
Security has been stepped up in Donetsk, where thousands of pro-Russian supporters are rallying on Saturday.
And in Moscow, about 50,000 people have rallied to protest against Russia's intervention in Ukraine, shouting, "The occupation of Crimea is Russia's disgrace" and "Hands off Ukraine".
A rival demonstration within sight of the Kremlin attracted an estimated 15,000 people in support of Putin.
The peninsula of two million mostly Russian speakers is widely expected to vote to split from Ukraine and join Russia after its politicians declared independence from Kiev earlier this month.
Kiev has denounced the Crimean vote as illegal.